There used to be a very good article by Dr. Fred on the TCCOA site. I used the basics of that article to upgrade my '94 auto back when it had only 15k and, now I have 140k with little or no problems. The basic issues with the early '94 - 4R70W auto trans were:-
1).Shudder from the torgue converter when shifting - basically resolved by flushing the standard Mercon fluid and upgrading to Mercon V.
2.Upgrading to the '96 valve body or installing an after market shift-kit, like Transgo (which I did).
3). Replacing the stock accumulator pistons (which were alum.) to the standard steel ones and removing the bottom return springs. With mileage in the car you will also need to polish out the score marks in the bores with a scotch bright pad.
4). The MLPS on the side of the trans (shift mechanism) had a bad gasket and was prone to letting in moisture, so replace it with a later version.
5). Install the larger '96 pan & filter - sometimes you can find a '96 pan which also has a drain plug (useful).
6). Replace all 4 of the solenoids with '96 ones.
7). Optionally replace the drive shaft with a balanced alum. one; especially if you drive it hard or have removed the speed limiter.
Hope that helps, but try and find Dr.Fred's article (very detailed)