88 Suburban Error code 42???

Hello everyone, I have a stumper that has baffled me and even three other mechanics. I have a 88 Chevy Suburban 5.7 350, there has been a problem with the vehicle for about a month now. The burb will start up fine, but after driving for about 10 minutes the "Check engine light" comes on and the vehicle starts running horriable. You can actually feel the thing struggling to fire correctly, there is no power in the pedal and it dies when you slow to come to a stop. Error code 42 continues to show up when I run a diagnostics(Engine spark timing). Now being moderatly familiar with trucks (I attempt to do all of my own repairs, but have never been an employed mechanic)I attempted to fix the problem myself. Here is of list of items I have replaced or fixed.
New distributer
New distributer cap
New rotor
New spark plug wires
New plugs
New coil
New TPS (throttle position sensor)
New fuel filter

I have now exhausted my knowledge on what to do. I carefully read each of the questions and answers in the history on this forum, but I was only able to find one that contained information about error code 42, his solution was to change the coil, I have done so and still have the same problem. My next move will be to disconnect the cat and replace the fuel pump, my question is, would the cat or the fuel pump actually casue an error code of 42? Another clue is that the vehicle engine prior to the "check Engine light" comming on, will idle fine and steady, but touching the pedal so that the vehicle just goes past idle, the engine sputters and wants to die, but if you gas it, it does great. Does any one out there have an idea of what I might do next? I would appreciate any help I could get, thanks in advance.

Hi. I just bought an 88 Silverado 1\2 ton w/350. The previous owner just put a new engine in about 1500 miles before. It ran fine for about a week. Then #42 & 43 came up. I have replaced the following:
ECM
IAC
EGR
ESC
Fuel filter
fuel pres. reg.
and checked each and every wire to and from the computer. Still no luck. If by chance you figure something out somewhere other than here PLEASE! post it for I am truly puzzled!
Thank you

if theres nothing wrong with the wiring at at the ecm and the distributor the cause of a code 42 is either a bad ecm or ignition module. some shops will replace both because it's pretty hard to determine which ones the problem.