Truck stalling out in gear????? 99 Yukon denali 5.7

[Genn15]

I started my truck this morning back to my driveway put it in drive and as I started driving If I was just intermediate with the fuel the truck choked as if it was running out of gas, But if I popped it back into neutral it would rev fine at any level I wanted it to and would hold it perfectly... So I put it back in gear in this time just left the gas peddle where it was and let it do it's thing and it bogged out and tried to stall, I started to realize it seemed it was shifting into too high of a gear .. I took the truck to the dealership had every mechanic in the place in it with me while we were driving And had their super GM factory diagnostic tool hooked up as well... It was reading that the transmission shaft output speed was through the roof and jumping like crazy... All of the other RPMs were perfectly in tune with the vehicle speed This one jumped at random at times up to 2400!!!! The mechanic tells me that that is only in full ton truck and I do have the LS 460 transmission he checked so my truck shouldn't have any reading there?? Or a transmission shaft output speed sensor to even communicate the speed? They told me they had no idea and then the dealership closed for the day When I left I pulled the fuse for the transfer case put it back in restarted the truck it ran fine for 10 hours I started and stopped it a few times even went home and made dinner was back in town later that night and it just started doing it again at random I tried swapping the fuse again but did nothing someone please help me I can't afford a transmission!?!?!?

 

[Donnie Yukonie]

Ok So let me try to get this straight In "N" truck runs smooth and great but as soon as you drop it in "D" it bogs down and dies? I don't think this is just a trans issue , Definitly Odd any CEL light?

 

[Genn15]

That exactly it. P430 but has been on and off for months

---------- Post added at 01:06 AM ---------- Previous post was at 01:02 AM ----------

And it doesn't die if u put in drive and don't move let it idle or accelerate slowly or accelerate very hard it run smooth shifts fine everything is great, try to pass someone without flooring it and it chokes and stalls

 

[Genn15]

If anyone cares to know for future reference encoder motor was sending single saying I was in 4 lo when I wasn't and it was shifting into top gear at 30km in turn causing it to stall without heavy throttle... As for the transmission shaft still a mystery I guess

 

[Phone Man]

Thanks. I have a similar problem. I'll be looking into this.