89 4.9 2wd - Need help, killing on acceleration
 

I have an 89 with a 4.9 2wd It starts good and idles good, and runs good til you give it acceleration, then it'll kill and you'll have to wait about 5 to 15mins before you can crank it up. I haven't been able to drive it since October. Since then I've dropped the fuel tank, cleaned it out and replaced the fuel pump along with external fuel pumps and put a new fuel filter on, replaced EGR valve, whole distributor and ignition but yet the problem still remains. I've taken it to a mechanic and he replaced all the vacuum hoses and checked and placed new wiring but couldn't find out whats wrong with it. So he ended up turning it down. I'm left with trying to figure out the problem but I'm stomped on what to do now. I really could use the help here. I would greatly appreciate any help I can get. Thanks!

Is the truck fuel injected or carbed?

Sorry forgot to mention. It's EFI, the mechanic also checked injectors and they are working properly.

Have you replaced the fuel regulator? What's the pressure you are getting at the fuel rail?