2006 Colorado Transmission Issues

[capecodken]

Colorado Transmission and high idle
Intermittent problems when I start my 2006 Chevy Colorado 5 cylinder 4x4 sometimes it idles high it doesn’t matter if it’s hot or cold then my auto transmission takes a while to shift into 1st. Then everything is normal for a month or so then it acts up again. I took it to a Chevy dealer about six times and said they can’t find anything wrong with it. No codes show up at all then I took it to amcco transmission and told my trans is ok but they said one code came up PO128 coolant temp below regulated temp. Now keep in mind this has been going on for a long time about 100,000 miles so far. This is the first code that ever showed up do you think that has anything to do with it? Also I know as soon as I start it and if it revs a little high, I know sure enough the transmission is going to act up again. Anyone out there have any idea’s what I should do.


Follow-up

Well all of a sudden the forward sprag assembly went and had it replaced I had no drive or 3rd but 1s t, 2nd, and reverse worked. Was relieved to find the problem then
All was fine till today, again sometimes it idles high and sometimes it doesn’t, and it doesn’t matter if it’s hot or cold then my auto transmission takes a while to shift fully into 1st. The code I got was P0442, and PO128 before the transmission was fixed and was told it is the gas cap, for PO442 replaced it, and code is still on also remember the code P0128 well that’s gone for now. I have no idea what to do about this. I just spent 1500 dollars to have the forward sprag assembly replaced should I also replace the coolant temp sensor. Any ideas???