The killer is your 3.90 rear which is a drag racing rear and not good for cruising. I'd replace that with 3.55's and keep the 4 speed (if it's an M20) and have a nice compromise with cruising and acceleration and keep the coolness of the 4 speed. The rule of thumb for final drive ratio in 1st gear is 9:1. So even with the 2.87 first and 3.90 rear you will have 2.87 X 3.90 = 11.2 which is still pretty steep. The 3.90 rears were pared with M21's and M22's with the 2.20 first gear. If you end up going TKO, listen to Hank!