hi all, newby here. i'm trying to help my son with his 99 tahoe 4wd. the truck sat for about 6 months, ran ok before this. however now when you start it the first time of the day it rans and drives perfect for however long its running, could be 5 mins. or 2 hrs. runs great! but if it is shut off it will not start unless the gas peddle is held right to the floor, it starts and runs real bad, has allmost no throttle response,and stalls at will, putting it in gear stalls it out. took it to autozone had codes scanned had just every code it could have! anyone have any ideas? thanks, steve.