ABS light came on, and is now shifting hard - 2006 GMC Sierra

Vehicle Dynamic Control, measures inputs from different sensors ie: wheel speed from ABS wheel sensors, trans gear position & speed, Yaw rate, throttle position, etc then makes determination on how to best control veh in a certain situation (accelerating to hard through a turn, wheel spin on wet pavement, sliding during hard stops and such). Can do one or a combination of commands to recover an out of control veh like release brake psi to locked wheel (ABS), limit accelerator, down shift trans, even transfer shift power from side to side/frt to back on some models.

Maybe you have a bad speed sensor, its a shot in the dark but that sensor controls a lot of functions like the ABS, speedometer, check engine light can come on, automatics will shift hard or may not shift at all, o/d will flash. The video below shows a 1999 ford ranger automatic but if you check you might have the same sensor.

Dont think so here the ABS is a seperate computer,have you washed the car by any chance with a jet wash on the wheels this will often clean the sensors on the wheels for the ABS making the light go out

Sounds like more than one problem.
The ABS light is on to tell you the abs system is disabled due to a problem. Same goes for the traction control which could be related to the abs system problem. Both systems have to work together.
The temp gauge issue could be a faulty thermostat or the cooling system could be low on anti-freeze.
The shifting problem could be related to either system.

I have the same problem in my 1994 Ford f350. I replaced the ABS sensor, but it is still shifting hard and the overdrive light still flashes until I shut the truck off. Any ideas?

Sound like a problem with speed wheel sensor, confirm this consition scanning the ABS module to know fault codes stored there.

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Scanner connected to the car that can look at the ABS system will direct you which way to start looking but won't fix the car experience mechanics the work on ABS won't be guessing and wherefore save you money by the time it's all said and done.

Have somebody check for trouble codes.Look for possible speed sensor codes.The speed sensor is a input to both trans and abs.

youll need to scan for transmission codes. the trac off light is a default of the trans going into a default safety mode. Bad speed sensors and simple little bolt on items like that can cause the condition but only way to really nail it is with a computer.

ABS light is on & Trac off light is on. Transmission does not seem to be shifting with any problem. What should I look for?