1990 Silverado starting problem ***HELP***

Hi any help would be appreciated because lord knows this has been nothing but a major pain in my ass. This started about a year ago during the winter and it is a mind-numbing problem. Ok I went out one morning to get the truck running turn the key and it turns over for about 2.5 seconds and fires up and immediatly dies. Then I turn the key again and and it turns over for about 1.5 seconds fires up and immediatly dies. Turn the key for the third time and either it will A)Fire up right away and die immediatly and wont fire up anymore just keep turning over and ignition stumbling, OR B) Fire up right away and idle real low and the engine stumbles real bad and it sounds like its misfiring in every cylinder but it will run for a while and eventually run smooth. I never knew when it would do this. One morning it would start up the next it would do this shit. I got it in to my mechanic and he had it for a while. I told him to let it sit outside for 3 days and try it, started up for him. Then I told him to let it sit over the weekend and try it again monday morning, THEN it didn't start up for him. He brought it in the shop ran all kinds of compression tests and everything else on it and could not pinpoint the problem. He said his best guess was the idle-air-control valve. He replaced that valve and I never had a problem with it doing this again. That was about a year ago. Three weeks ago it started doing it again. Same exact problem. I pulled it into town to my mechanics and lefgt it with them. They had it for a week or so and I got it back. He replaced the idle-air-control valve again. It was fine for about a week, I thought that took care of the problem again but now it is doing it AGAIN. DOES ANYONE HAVE ANY IDEA WHAT THE HELL THIS COULD BE? What is causing this? like I said any help would be appreciated because this truck is my only vehicle. Its been a damb good truck and never let me down before until this. Thank you for checking this out and help me if you can.

well fuel air and spark.... it sounds like u have spark.. so have u checked fuel pressure???... and give me a lil detail on this truck