Chevrolet Repair: 95 chev. silverado 350 5.7 4wd continuous problem, gm dealer, continuous problem

Question
For the past few years, I have had problem with rough idle. In trying to find the problem, I have had it to 2 GM dealer mechanics as well as 3-5 local mechanics.  In the process, I have allowed them to replace, even re-replace everything, and even I have installed various parts (gm - water in gas to can't find - so replaced computer). Can never duplicate the problem, but out of respect for all trying, I have allowed these replacements - including all sensors, new distributor, new jets, etc. I can go on but it's boring, but you name it and it's been looked at.
Maybe you can mention something to help.
It will run great for a while 1000 -2000 miles, go out to start up and seems like not getting gas, pump and try, it may start, but rough idle and finally die.  I mess with it, got a code 42 last time, replaced the knock sensor (last of replacements).  Hooked back up, ran good for 3 days, @500 mi and a few startups. Yesterday, rough startup, for the first time got a code 51?  But, gm replaced the computer 10 months age. Finally, would not start at all - seems like no gas (fuel pump replaced 6 months ago).  It's raining, but I plan to go out and tinker again, hoping!
Really, this is difficult to explain, but I hope you get an idea. Would appreciate your positive input.  It's something, but I love my truck!
Thank you should you consider a response.

Answer
HI RICHARD, WELL THIS IS A HARD ONE TO ANSWER BECAUSE IT COULD BE ALOT OF THINGS CAUSING THIS..
WIRING HARNESS COME TO MIND. A BREAK OR ALMOST BROKEN WIRE MAY CAUSE THIS IN A HARNESS..THIS TRUCK WOULD NEED HANDS ON TIME TO DIAGNOSE.. WHEN IT WILL NOT START OR CRANKS OVER FOR A LONG TIME HAVE YOU CHECKED FOR FUEL PRESSURE AND SPARK ??? IF ONE IS MISSING THIS WILL GET YOU IN THE AREA THAT YOU NEED TO LOOK AT..HAVE YOU OR THE OTHER TECHS CHECKED ALL OF THE GROUND WIRES TO THE ENGINE AREA.. BAD OR LOOSE GROUNDS WILL CAUSE THIS TO HAPPEN AS WELL. CARRY SOME STARTING FLUID WITH YOU IF IT WILL NOT START GIVE IT A SHOT AND SEE IF IT WILL START LIKE THIS. IF SO YOU KNOW IT IS A FUEL PROBLEM..I WISH I COULD SHED MORE LIGHT ON THIS BUT AGAIN THIS IS HANDS ON FOR SURE..YOU HAVE TO START WEEDING THINGS OUT...GOOD LUCK TO YOU,AND IF I THINK OF SOMETHING I WILL GET BACK TO YOU..TOM....