Hi folks,history of truck:2nd owner,wife driven (to slow usually lol) 300k ,1st owner an older gent took very good care of it.We drove it for 10yrs then parked because of a fuel pump going bad and we live out of town.Due to a serious family problem we had to have wheels now,bought another truck.This sat for quite awhile but i started it twice a year just because.So ive retired and thought I would put this in shape for a backup rig.It worked great before but it will not go into3rd now.I pulled the elec.plug off and drove it.If i keep it in M2 it will shift into 3rd easily and you can lay on the peddle pretty hard and it does not slip, but if I shift to M3 I lose 3rd gear but it will go into 2nd if i slow down but will not upshift into 3rd on acceleration.Always works in 2nd tho,I have verified both a and b selenoids go off in M3 with a test light at PCM.My uneducated guess is something is stuck but i cant determine what because of limited knowledge (very limited).I do have the pan off and there is the black silt natually but only very light sprinkling of shiney metal.I know its rebuild time with the amount of K on this truck but i would also like to trouble shoot it too just for learning more.I do have a hoist which makes it easier to mess with.Any help I would be greatfull for,Ive been to a lot of forums and the answers to problems on here are unequalled anywhere ive seen.Thanks for your time.

 

Honestly with 300k miles I would not do a thing till I rebuilt or replaced the trans /

 

It sounds like there could be a valve stuck in the valve body. I would start with the 1-2 and 2-3 shift valves. If you have access to a scan tool, I would check that the gear positions indicated on the scanner equal the position of the shift lever. One of the shift solenoids could also be stuck.

 

Thats what I was kinda thinking, something stuck.I will check that and let you know.I know this is a kind of a lame thing to ask on this forum but after .reading other places its just 3-4 burnt clutches and this isnt yet.But I do agree I might be beating a almost dead horse.Thanks for the replies.