First time post here! I have. 1997 gmc serria 1500 5.0 v8 4x4. 150,000 miles I had a head gasket go. I took it to my local shop and spent some $$$ and had it fixed. Two new gaskets and had the heads shaved and tested. I got it back I noticed a serious hard starting problem when cold and stalling out when taking off. Also if I rev up the throttle response is off and it will stall out. Took it back and the tech said the computer went bad. $200 got a new computer. I still have the same issue. So now I’m leery of my tech. I had put his computer on it and check the timing and it’s perfect and it’s not throwing a code. What could it be? Throttle body issue, mass air flow needs cleaning????? Also have a spark knock and I tried all octane levels gas and no real difference

 

Hi. Without any codes sure makes things harder to diagnose. It should eventually generate a code since stalling is certainly a serious operating condition.
From cheapest to costliest, I'd look at: 1) fuel filter clogged, 2) fuel pump pressure, 3) plugs & wires, 4) fuel injector assembly (aka, "spider" assembly)

 

no codes yet! The plugs and wires are new or less
than 5k on them. I was wondering about the injector system cause there is a new system that changes to multi port injection from single if I remember correctly. Fuel filter was changed probably 20k ago but that’s an easy item to cross off.

 

I would definitely not trust a shop which says replace the ECM without a code indicating ECM was dead.
With lack of code I agree with Czech to check basics - fuel and timing. ECM has no direct feedback on either so they have to be right.
However, if problem started clearly with pulling replacing heads, it may make sense to check or replace CTS and wiring to CTS. I don’t have experience on your year but I think CTS is on side of drivers head - and if it’s not accurate can cause problems.
For stuff like this, it’s worth getting a datalogger so you can see what the ECM sees - ie. What is it reading for CTs, tPS, etc