Engine Performance on 2000 Chevrolet 3500 Pickup

Have had checked and spent $ for fuel pump and etc. Engine light on engine. Engine has to idle for 2 minutes before there is any throttle responce, cold or hot. Performance fluctuates. Fuel filter has been changed. Tranny oil was changed.

1 answer 2 comments
With the check engine light on there should be fault codes stored in the pcm, do you have any idea what they are?
The last tech said it showed lean mixture. They could not tell if it was one of the 4 O2 sensors or a lazy one or what, Their best idea was to start changing parts until something worked. Sounded like a lot of money and practice for the mechanic to change parts. Thank You for your help.
I don't think your problem is releated to the O2 sensors because they are not in control of the system during initial start-up. If your engine is running lean on start-up I would begin by checking fuel pressure and injector flow. Another possibility is a coolant, or air temp sensor that is out of spec but not enough to set a fualt code.