Transmission problem

i have a 2001 montana 3.4l. i had it in the shop because when on the highway doing about 120 km/h the rpm is at like 3000 to 3300. they said that a code 1811 was in the computer ( tranmission maximun adapt and long shift ). if i have too much fluid in the tranny could this cause this problem or how can i fix it if i can fix it.
thanks
tommy

Ok, you had the vehicle in a tranny shop, and they told you the code was P1811......Did they road test the vehicle with a scan tool on? Did they check for slippage? Did they command a certain solenoid on 100% and check slippage? Did they tell you what the fix usually was, and are you asking us for confirmation?

Another symptom of this code is, coming to a red light, you slow down...but then the light changes to green before you come to a complete stop, and you start to accelerate and you may feel a shudder....

There is a TSB for this, and the "usual' fix is a new PCS, pressure control solenoid....but there also could be valve body problems.....

Can you do this yourself? Sure.....have you ever taken the side cover off a 4T65 tranny on a U van? Not easy....

Also, why would the trans fluid level be high? It's usually lower....have you been adding fluid? If you haven't, and all of a sudden it's getting higher, how is your coolant level? Been adding to it?