1995 Chevy Silverado I am all out of ideas

I asked the mechanic if he had checked the fuel pressure like you had suggested he said no that he would be getting to my truck over the weekend. When I called back he said he didnt have the right adaptor and would have to order the right adaptor and that he may have to rig it from the fuel filter and not from the fuel rail. So I am still at a stand still. I had gotten into my truck and turned on the key the check engine light is off but the abs light remained on but thats been like that for sometime. The mechanic said that he thinks theres a vaccum leak and that will take some time to trace. I dont see how since he shouldnt have touched any vaccum lines while doing the tune up. He said theres a crack on the exhaust manifold and thats where he thinks the leak is lol but its an exhaust mainifold and if the crack was deep then it would be blk cause it's for burned gas right. I think he screwed up and has no Idea and is just throwing things out there. Sorry for ranting I'm just frustrated and cant seem to get him to do what you suggested. And refuse to take possession of my truck till he fixes it.

When the mechanic had the truck running I did not hear anything off the exhaust manifold. I'll go over today and maybe spray some carb cleaner on the exhaust manifold where the crack is.

I called the mechanic and he said I have good fuel pressure but would not give what the reading was so Im not sure if he had done the test. I thought that the exhaust manifold was for burned gas, so what I had done was got a used one and changed out the gaskets. I went to the link you had suggested I look at. There was something mentioned about a fuel relay switch that should be changed each time a fuel pumpis put in, also the fuel regulator should be checked. I am not sure if that was checked. Would either of those cause the the performance problem im experiancing?

I swung by the shop today to see whats the verdict on the tests. The mechanic said he's checked the EGR valve? And said that the truck died when it was disconnected so its working. He has checked the intake manifold for a vaccum leak and said he has found nothing. He has not checked the fuel regulator or the relay switch I asked if he could check those today and let me know what he finds out. The mechanic said that the idle on the truck fluctuates it will idle then rev up then drop till almost ready to die then goes back to normal idle.
THIS IS A NEW DEVELOPEMENT SINCE THE FUEL PUMPS BEEN REPLACED. My truck has never done this prior. Should I take my truck to a different shop with someone my certified?

Thank you for all your help and advise. I will be taking my truck to a different shop.