91 B2200 5spd Mess

I bought a solid 91 single cab b2200 5spd for $750.00 and was told and shown receipts for a new top end, timing belt and timing belt idlers. It ran good so i bought it, on the way home i noticed a large puddle of oil and determined that it was the front seal, replaced it and fixed the problem. Tail lights flaked out so they got rewired. Dim headlights and dash lights, was a broken ground wire off of neg batt cable. Now I am STUCK. When starting on cold mornings 20 deg F and letting it warm up for 20 min it runs very rough for about another 20 min. 2) When driving at a constant speed the engine will sputter, sounds like a miss fire, add some acceleration, it goes away. 3) When idling or driving at hwy speed with heater off temp gauge is normal/high-normal. When the heater is turned on it goes all the way HOT, shut it off it begins to drop soon after. Any help would be awesome.

First thing I would do is install a $20 aftermarket temperature gauge so you know exactly how hot the engine is getting. It could just be a whacked out factory temp. gauge and if so, a new temp. gauge will let you know. You don't really need to permanently install it, just hook it up so you can watch it as you drive the truck.

There are a couple of screwed-in plugs on the side of the aluminum intake so you can remove one of them and install the sensor bulb in that hole.

Here's how my B2200 is.......

Like Earl said: check the engine temperature/thermostat for correct warm-up.

I'd also make sure the choke butterfly/choke is working correctly (choke heater wire plugs into rear of the alternator), and make sure the EGR valve is operational when vacuum is appled and actually closing all the way (these tend to carbon-up and stick and need to be cleaned).