I bought an 88 conv vette w/43000 miles with the nash 4x3 tranny. I did'nt do any homework prior to buying, just got ate up with the test drive. I paid 9500$ and thought the car was a good deal. Now a month later I am reading about numerous troubles and expenses with the overdrive units. I hope I did not buy trouble. I am looking for experiences and imput, I am scratching my head wondering if I should sell?  

The 4+3 was not a very good design. That being said, if yours is in good working order, and because of it's low miles, here's what you can do.

Option 1 is to stick with the 4+3. If you stay religious with changing the tranny fluid and other servicing on this tranny, you should be fine. These transmissions had a low tolerance for poor service habits by owners.

Option 2 is to talk to Keisler about one of their 5-speed conversions for C4s with 4+3 transmissions. Their kit is a direct bolt in, and if I remember correctly will fit in the stock transmission tunnel. The onyl change is the driveshaft and probably the transmission mount.