I'm new to the forum, but have owned my 2005 HR since 2008. 237,000 miles. Rebuilt HD Trans at 163,000 with HD Trans cooler, rebuilt water cooling system, and complete front end rebuild. Ran great till this year. Check engine light came on and have been chasing issues since;
Here is what I have done so far:
New spark plugs OEM & new wires - ran smoother for two days then went down hill. Now it not only runs rough with the check engine light coming on and going off, but the transmission is not shifting correctly. Note: it's less than a year old with a 3 yr/1000,000 mile warranty so I'm confident in it. Is it possible the rough idle and rough running is preventing the trans from shifting correctly?
Any suggestions on chasing down the rough engine issue first? Once that is corrected if the trans still shifts bad the mechanic will take care of that issue.

 

Sorry for the typo - just noticed. I have a 2005 H2 not an HR.

 

so when you say not shifting correctly, how, from 1st to 2nd or, in and out of top gears when going down the road? Did the engine over heat ever?, what codes are you getting?

We salute you for your patience and love for a machine that loves money thrown at it after getting you this far up the miles scale.

Does the engine lose power at low speed driving and maybe you think it's the transmission playing with you cause the vehicle bucks and the throttle is sluggish.

Maybe, just maybe it needs a pcm check and reflash from the gm dealer.

 

Check the MAF to make sure it is aligned property and test it.

What codes are you reading?

Tim

 

Yes check the DTC codes and history.

 

I agree you really need to pull the codes. Have you ever replaced the catalytic converters ? They could be plugged with that many miles.

 

Indeed, happened to my 2005 H2, the CATs turned into buckets of sand.