5.7L Vortec issue
 

I have a 1997 Silverado, with a 5.7L Vortec and recently the engine has started to stumble and hesitate during acceleration and heavy load. I have recently replaced spark plugs, cap and rotor and fuel filter and haven't seen any improvment. Any suggestions?

I would check the fuel pressure. Those also have a spider type fuel injection that is known to go bad. Is it hard to start?

It starts and idles fine.

The check engine light is not appearing and I didn't find any codes when i scanned.

A weak fuel pump would not necessarily trigger a CEL. The spider injection could be causing that. I have had to replace a few. Also you did not list plug wires...a bad wire could cause that as well. I would still do a fuel pressure test though.

you also could have a vacuum leak at the intake gaskets or a bad vacuum line.

I agree with mr. shamrock sounds like a fuel problem. It is possible that it is the fuel pump.

Recently I have started to get the check engine appear under heavy acceleration. I scanned it and it shows that I am getting low voltage readings on both pre-converter 02 sensors.