I have a 2000 2500 chevy 4x4 with 130,000 miles. The check engine light comes on when I'm running down the interstate at higher speeds, or when I pull my bass boat. The tranny temp gets up to about the same as the engine temp (200 degrees) and it starts shifting really hard. The code for the check engine light (I think it was an 1876 code) says it is slipping in O.D. according to the parts place. I use my tow/haul button anytime I'm pulling. It has been doing this since about 95,000 miles. It doesn't seem to be getting any worse, but it is irritating.

When I drive it to work or around town for a few days the check engine light will go off and it does fine. It only seems to shift hard though when the trans temp gets high. Anyone have any suggestions on what I can do to fix this other than a rebuild or new trans?

6.0L engine, 285/75/16 tires