1999 5.7 2500 Service bed
Rough idle dies when you hit the throttle . No codes Fuel pump/filter checks out. constant 63 psi. No vacuum leaks. control module/coil checks out. Cap and rotor checks out. I'm at a loss. Did not die on road. drove home fine no issues next morning no start. Truck has 160k miles did run excellent. Was smog 2 weeks prior. Smog guy was surprised how well it did.(tight motor)

 

Check the fuel pressure regulator to make sure that the internal diaphragm has not ruptured.

 

Double check the TBI gasket

 

A 1999 isn't going to have a TBI.

It could however be a bad fuel pressure regulator. The problem is GM put the stupid thing under the upper intake manifold. There is an R&R video on youtube showing what all is involved to change it. The symptoms you describe are identical to my 2002 van which I believe had the same problem, a bad regulator. I say I believe because I never changed it, the idea of a four hour job messing with plastic parts doesn't appeal to me much.