Engine cuts out at high rpms.

My 87 B2000 is having a weird problem, it runs great up to 4500 rpm but once it gets there it just cuts out until its back to about 4000 rpm then goes back up to 4500 again. It feels like its hitting a rev limiter of some sort. I put a brand new fuel pump, fuel filter, all fuel lines, and a Weber 32/36 (it did this with the stock carb also). It is getting plenty of fuel so that means it must be an ignition or ignition timing problem. It has very strong spark and the dist timing is set correctly but something I noticed is that it runs the same with the vacuum advance disconnected so I'm thinking this could be the problem but I don't have a timing light so I can't test it properly. Do these trucks have any kind of ignition control module or anything else that could cause this problem? I don't think its anything mechanically wrong with the engine because it sounds fine and runs great all the way up to 4500 and when it cuts out it doesn't make any bad noises or anything it just feels like you turned the key off for a second and then back on. So if anybody has any suggestions on things to check I would greatly appreciate it. Thanks

Edit: Also I forgot to mention that it runs the same with the exhaust disconnected so its not an exhaust restriction. Another thing I forgot to mention is that it does this in neutral and under load.

My first questions are:

1. EGR? How clean is it?
2. Vacuum leaks? Do you hear any hissing? If you start it and spray some starting fluid along the lines, does this make any difference?

I don't exceed 4500 rpm on mine.

I would check with a timing light, make sure that the timing is advancing as rpm increases. Has your fuel filter been changed in last 2 years?

Doesn't have EGR anymore, and as far as I can tell no vacuum leaks. I resealed the entire intake just to make sure (intake manifold gasket, carb base gasket, pcv valve and grommet, all new vac lines.)

I don't usually exceed 4500 rpm either, I just like everything to work like its supposed too. The fuel pump, filter, and all the hoses are brand new. I guess I'm probably going to have to go buy a timing light since I'm pretty sure this is ignition related.