GMC Safari

Hello I have a 1999 GMC AWD Safari with 124000 miles. I have no codes, hard or soft. After car sits overnight I have to crank it repeatedly before it will finally start. Once it has started, it continues to run and will start normally, until it sits again. I have checked the fuel pressure it is fine maintains about 55 lbs and holds pressure after shutting off engine. If I pour just a very little amount of gas into the intake the vehicle will start and run. It seems now to be missing or backfiring when I get it started now and then tromp on the accelerator. The tail pipe looks to be running pretty lean. I am at my wits end, after searching exaustivley on the internet. I unplugged the throttle positioning sensor and didn't seem to make a difference. Hope someone can help. Thank you, John
June 17, 2007.

First try checking your spark plug gaps on all cyls. If you have havent changed your plugs. If you havent I recommend you do it that way you know you have clean and correctly gaped plugs

Cesar lomeli
Jan 14, 2008.