I'm just getting the parts together to do the 3.89 gear swap on my Intrepid. I have a '98 3.2 ES with autostick.
I have read that any '99-'01 TCM from a 2.7 will work to fix the speedo and retain the use of the autostick. I also read that if I get a '98 TCM it has to be from a 2.7 with autostick. Are these two statements true?
The gearing is different by about 7% - so everything changes by about that much - BUT - with autostick you can go one of two ways... you may drive it like you stole it because it is autostick and fun to do, and in that case you stuck because driving habits will affect mileage the most - but then again, you may GAIN mileage because you may find better shift points. With the gearing difference you can see similar problems of having more 'fun' with it and putting the mileage in the tank.
As for changing the gears - it can be done with the engine in the transmission and the car on the ground - I'll try to find the How To for you.
You will lose 1 to 2 mpg I found. Your big loss will be on the highway, in the city it might actually help the gas millage because it's easier for the car to get off the line so the engine forces less. Price all depends what kind of deals you can find, figure 200$ max usually.
Here it is the how to... this is for the 1st gen, but the 2nd gen is the same transmission - but the mounting process may be slightly different. I would suggest draining and changing the filter at the same time, since you're going to have the transmission open and losing a lot of fluid anyway.
How much money are we talking about to do this swap? I see the gears are about $80, what kind of labor is involved? How bad does gas mileage suffer?
I haven't put them in yet so I can't tell you anything about mileage, but I got everything I need to do the swap for about $115 (TCM, and gears). That was without really scavenging around trying to get the best price on everything. I'm sure you could do cheaper if you wanted.