Running horrible--help diagnose? Please?

93 B2600i, FI

Here's what it's doing, and I ran a can of SeaFoam through it 2 months or so ago with problems starting right after (no I don't blame the SeaFoam, but could be relevant), it does burn oil and I believe it did/does burn some antifreeze as well since I always had really heavy white vapor in the mornings and slowly lost antifreeze with no other visible leaks.

Runs rough, sounds like it's missing, lots of vibrations felt in truck.
Originally it would run rough/bog till about 2k rpm then take off like normal.
Used to get worse when hot.
Didn't like hills--coughed, bogged down, sounded like it died if too much gas but would still go up them with miniscule adjustments on throttle.
Now barely idles--have to feather gas to 3k to start in 1st, anything less and it bogs and nearly dies.
Always sounds like it's missing, even over 2k--though it still runs better over 2k
Whole truck shakes with vibrations with how rough running it is under 2k
Runs marginally better the warmer it is now.
Won't do hills--I loose speed and can't give it more gas since it bogs, sounds like it dies and looses all power (same under 2k)
Stopped putting out white smoke when warming up, or blue smoke (but I need to check the oil again)

Any ideas?

just keep an eye on the coolant. i had the same issue up to 2000 rpms and mentioned it on my thread. clean the egr valve under the carb on intake (3 10mm bolts note where metal gasket goes. then clean reed valves where the three hoses connect to intake. and i dont know if u will wanna hear this but i unplugged the wire harness closest to the passenger seat from the ecu under passenger kick panel. idk y it helped but it did. when i plug it in the truck barely starts and shakes like crazy when i rev it and fell on its face untill 2000 rpm. so i left it unplugged and left the one closest to firewall plugged in. then i just checked the regular, cleand plugs, double checked timing ect. some say the surge your describing is from a lean air fuel ratio. im not sure maybe u can find some info. and maybe clean ur o2 sensor if u leave the ecu plugged in. if u do unplug it, do it with the truck and key off. sorry for the book. hope this helps

I'm running efi, so nothing under the carb. . . and not sure I can get away with unplugging the comp. either.

oh shit yea probly not. lol i assumed u were carbed. sorry im not much help man. i dont know much about efi. do u burn oil. i burn a good bit of oil and if i dont clean my plugs within 3 weeks to a month my truck will start sputterin n stuff. kinda like a 2 stroke when it fouls plugs. other than that good luck to u.

Sounds like you've blown a head gasket too, and/or cracked the cylinder head. Pull the plugs and take a look. Check the compression. If it will idle, you can pull a plug wire and see if any of them has little or no effect at all. That would be your bad cylinder(s). I don't think I'd drive it anymore. It's not gonna fix itself. You are probably running on 2 cylinders.

Check for any vacumme leaks or for a bad maf sensor aswell with the cylinder compression test... Also perform a leak down test to ensure it is indeed a cracked head/head gasket

Checked the plugs, all had a grayish white coating except #1, which was loose and looked kinda oily-I swapped it out with a new one. Runs marginally better above 2k.
I've had a valve leaking oil for as long as I've had it. Thinking maybe injectors are fouled? Or my leaky valve is no longer seating properly?

I plan on doing the cylinder head sooner now than later, but want to make sure there are no other probs first.

Update* got a few seconds of normal power and all cylinders firing this morning while in 1st surged a bit over 3k. Thinking it's either fuel or air management.

Whats the best way to clean the MAF sensor?

Throttle body cleaner... NOT carb cleaner... CARB cleaner puts a harsh coating on sensors... If you have a vaccume leak, between MAF sensor and throttle body, you would experience some of the symptoms you have been experiencing... Pull out your multimeter and ohm out the injectors and give us you readings..... Generally speaking, if the injectors are all about the same ohm readings they are fine

They even make a MAF cleaner now. You just spray it on. There is also a test to check the voltages on MAF as well as the rest of the FI components.

If you were having white smoke, then I'd still be suspect of head.

Could have a computer problem. A bad one can give lots of different problems.

Do you have any signs of coolant in the oil? Oil in the coolant? Look in radiator neck and in overflow/recovery tank.

Btw, I think it might have been you that mentioned your idle speed changing when you put it in gear, even with the clutch pushed in. If that was you, then you have a problem with the clutch switch or neutral switch. You shouldn't see any rpm change.

I've owned my truck for almost 20 years and I've never seen it do that. I was also helping the other member on here with that problem troubleshoot the condition. His turned out to be the clutch switch.