Check engine light is on for my 2006 GMC Sierra

Make sure you have good ground not only to the engine but from either battery to body and chassis or engine to body and chassis.

Take it an have it diagnosed rather then looking for a magical fix on here ! Without testing , viewing scan data ,we would only be gussing . We could suggest a number of thing's that could cause this . Are you willing to replace parts that may not fix the problem. (waste of money ) !

That is really low mileage for issues but clunking into gear is a symptom of a bad universal joint on your drive shaft. Does it clunk in D and R?

Do you have a service engine light on? If so the first thing to do would be to check for what codes may be stored.
You can also check for vacuum leaks. A good place for a leak is the TB base gasket. Those start to leak and give a fast idle.
As for the late shifts, just about all you can do is check fluid level. The shifts are computer controled. 93+ trucks have the 4L60E. Not even a TV cable to check adjustment on.
Fix the fast idle and the late shifts issue may go away.

You need a dealer.

I would look into the coolant temp sensor .
As it sounds to me that the auto enrichener (choke) is letting go too early.

Check that , and let us know what you find !

Thanks!!

little red light on right side of rear view mirror is on and dome light, temp gage, on star--nothing works

More than likely the evaporator vent valve.

Check engine light will go out when the management computer detects no more errors. Pull the codes and repair what they indicate.

Sounds like an oil pressure problem. The clacking sound is most likely the lifters are collapsing due to loss of oil pressure. You may have a failing oil pump.