I30T trans issues...

[atr-drivr]

Having shift issues with my 00 I30T. Seems like no power when it shifts into OD on the highway and then all of a sudden will downshift as it goes up a very slight grade. Was attempting to pass a car, stomped on the gas and it did nothing. RPM stayed at about 2200, no shift, no power. I grabbed the shift lever and dropped it into low, second and D and it did nothing!!! Almost got nailed by a big rig. Dealer had done an $800 "adjustment" a few months ago and now says it might need a TCM. Is that able to be changed in the garage or needs to be done by a dealer?I changed the starter the other day in about 30 mins for only $150, dealer wanted almost $500.... Thanks