I Have a 86 300sdl and at 55mph my rpm is 2100, at 60 it is 2400rpm
at 65 2700 rpm and at 70 mph it sits right at 3000rpm. This is totally normal. This car was designed when the national speed limit was 55 mph. Now that it is 70 or 75 in places, you will notice 3000 to 3300 rpm at those speeds.

I have no lag when I place my car in reverse. My car has 104,000 miles and I change transmission fluid and filter every two years religiously.

John