Can you advice me as to what best application 4-5 or 6 speed Application would apply. Currently using 1977 th 400 3 speed on a 896-2 Diesel. Fr having trouble with engine over Speed @ 65-75 mph. :( not good anyways heard the All: Son is best. Hunting 7,000 lbs trailer on p 30 Step run chassis. Any Adivicc would b good.