Since it has gotten cooler here in Texas i have noticed the engine running at higer RPMS at speeds 2-300rpm higher than normal. I thought it was just when the engine was cold, but yesterday driving on a road to my house at 42mph in cruise control i noticed my tach running high, tapped the towhaul mode and the trans locked up 2-300 rpms lower.

Is this normal?

How many miles did you drive it? It sounds like the trans wasn't warm enough to engage the torque converter clutch. The fluid temp has to be about 75° for it to work in normal mode. The clutch is engaged more in tow/haul, and the temp threshold may be lower as well.

Last night was after 30 minutes and 20 miles unloaded.

With mine, it does the same thing. RPMs run a little higher, until trans temp gauge hits first mark. Then RPMs drop about 2-300 ish.
Believe it is to help trans develop temperature, for operating.

Won't let the Torque Converter lock up until a certain trans temp is reached - running unlocked generates more heat.

I guess its something i have to live with in these chilly winter days in Katy, Texas.

These trucks need winter BRAS, the rad areas are so large they don't get a chance to warm up.

good luck

72 outside today that's ruff ain't it. Mine acts up when it's cold until it gets warm.
Scott

Mine does too when it cold, but warmed up and 50 degrees outside. Just not sure why it seems to be slipping.

I installed a oil pan heater on my tranny. Works great, even when it's sub zero tranny works just like it's supposed to. You can get the 125 Watt kit on E-bay.

BMCD,

Read the attached TechLink, and the paragraph just below the "Sump Temperatures/Ranges Available" chart will answer your question:



http://service.gm.com/gmtechlink/images/issues/aug04/TLaug04e.html


Good Luck!
Gary

BTW---I'm only about 100 miles west of you.