2013 Sierra crew cab 4X4

[Barry Hanback]

My Sierra, when climbing a steep incline suddenly goes out of gear, engine revs and truck rolls back down. I tried several times with the same results. No codes. I turned it around and backed up the same inclines several time with no issues. Trans is a little overfull of fluid. Also I tried 4 lo and the truck started buck jumping along and died. I will not run smooth in 4 lo, just bucks along till it dies. Still no codes. Any ideas?? Thanks in advance.

[richard wysong]

Are you checking the fluid running in park? If so I would drop the pan and see if the filter is in place and clean. If that checks out you are probably looking at rebuilding the trans. Does it do it in 4 hi as well as 2 hi?

[Barry Hanback]

On 8/1/2025 at 1:38 PM, richard wysong said:

Are you checking the fluid running in park? If so I would drop the pan and see if the filter is in place and clean. If that checks out you are probably looking at rebuilding the trans. Does it do it in 4 hi as well as 2 hi?

It just does it in 4 hi cause the incline is grassy and too steep to try in 2 hi. 4 lo it just buck jumps and goes dead. It won't even hold back on a grade in 4 lo without bucking bad.

[richard wysong]

Could be the chain in the transfer case jumping