Oldsmobile/Buick Repair: 2001 Intrigue transmission, torque converter clutch, worst case scenario

Question
My 2001 Olds Intrigue has a 3.5L 6Cyl engine with automatic overdrive. Until recently, when I approach 45mph/2000rpm, the car shifted into overdrive and my tach would read 1500rpm...I could get to 70mph @2000rpm. Now, it doesn't shift and I'm doing 2500rpm @ 55mph.
Q1 Is it dangerous to continue driving without fixing?
Q2 How bad/expensive is it to have this fixed?

Answer
Hi
As I state in my Bio I am not the greatest Tranny guy.
I can tell you first I would get the computer scanned for codes.
Some transmission codes WILL set as Type c or d codes so they WILL NOT turn on the Service Engine Soon Light.
There are a few things it could be.
Any internal hydralic circuit in the transmission that applies the TCC (Torque Converter Clutch).
** Automotive Lesson for You**This is what actually lowers the RPM's. It shifts into 4th then the TCC applies. It is exactly what is states. A clutch in the Torque Converter that applies. When it applies, it "slows" the converter down, which in turn slows the engine RPM's down, IN FOURTH only. If TCC was stuck on at all times, the engine would not be able to spin fast enough and stall out.***
OK So the TCC Solonoid could be faulty (Not turning on)
The Torque converter COULD be at fault.
The PCS (Pressure Control Solonoid) in the transmission MAY be bad (Controls hydralic fluid line pressure - VERY IMPORTANT)
So these are just a few things.
Best advice.... take it to 2 or 3 different shops and maybe a transmission shop or 2.
See what they say.
I would not be suprised at all if the PCS is faulty. You would USUALLY experience a few other different symptoms but faulty pressure will create numerous problems.
To answer questions
1) cannot say depending on ACTUAL problem...but from what YOU say and without actually driving car..probabally OK to drive, just fuel economy will suffer on highway trips.
2) same answer as above,... worst case scenario... new transmission, $3500.00 or there about for a SRTA and labor.
I really hope this helps.
Please, if you need more help. feel free to follow post back.
Good Luck
Pawl