I have a 2000 2wd, started noticing a slight lag in started from a dead stop. I soon noticed the service engine soon lamp on coupled with the o/d not engaging. What the hecks going on? [/align]

 

Is it shifting at all?..Sounds like you may be taking off in 2nd and staying there..
'
When a gm truck has a trans fault,it "defaults" to 2nd gear.....

 

You have a 4L60E automatic. And your 1st and o/d shift solenoid has failed and needs replacing.
If you go to a big auto chain like autozone they can scan your car for codes for free.
The repair is about $500, and if youneed toask what it is, your probably not going to be able to fix it yourself.

Good luck
I can get more imfo on this topic if it will help.

Bill

 

Thanks for the advise. I went to autozone this morning and bought a hayne's manual. Look at the wiring diagram as well as pulling the OBD. 1-2 shift solenoid. Might have tackled in my younger days, but after two back surgeries, better left to the pros. Put it in the shop today and was given a $200-$300 estimate. Thanks again.
PS After assessing again this morning, it was indeed starting in second and then shifting to third.