Fuel presure in tbi injection system is 14 psi If the engine doesnt start easy ,you can try cranking the engine and depressing the accel to full, that permits the fuel cut and the fuel flooding ignites.
fuel pressure is 10 psi like ed said, and that pressure is maintained by regulator behind injectors on fuel meter cover,check fuel pressure, there should be shrader valve on return line to attach gauge to,the delay in throttle plate movement sounds like worn governor activation gear, disassembly for inspection required to confirm condition-check fuel pressure 1st, also as truck is being cranked check tbi injector spray pattern with timing light, you should see a nice uniformed spray cone underneath injector, any excess dripping while cranking,running -bad regulator, dripping after shut off also caused by leaking injector or upper fuel meter gasket or cover, also check engine oil for excess fuel and change oil if oil is gas washed or engine damage will occur
I think the fuel pressure on these is only about 10psi at the injector , (hopefully someone can correct me if I am wrong) and most mechanical and after market electric fuel pumps make about 18PSI (and up).
I haven't been back yet, but I did pull out my old fuel pressure test kit for the next time I go back to it. It has a spring & diaphram regulator built into the TB assembly and a return line back to tank, like many modern MPI injected auto engines, so if there is an over pressure problem its probably a restriction in the return line. Unlike automotive fuel injection, it doesn't have a vaccum line to the atmosphere side of the FPR, so its not designed to alter the pressure with engine load. It does have a MAP sensor to gauge engine load, and they are cheap so I've already ordered a new one, and I plan to replace the vac line to it when I replace it. I've also ordered an ETC since they are also cheap, and a known failure point on GM engines (and a faulty ETC will often make the ECM think the engine is ice cold and therefore over fuel the engine). The injectors have no visible fuel flow when unplugged, so I think the Orings are ok, and since they are above the throttle plate they wouldn't be a source of vaccum leak. Speaking of vaccum leaks, I should probably replace the pcv and its rubber grommet in the valve cover too. There isin't much else on this to to leak vaccum other than the intake manifold gaskets, and I don't even wan't to think about that.
have you checked the fuel pressure from the pump? (not too much pressure) and have you checked the o-rings on the injectors?
and have you closly checked for vac. leaks?