Given your tires are 26 in tall with your set up 50 mph you'll be turning 2,500 rpm , just coming on its power band , 3000 rpm will give you roughly 65 mph
which will make the 6 cyl music a little louder , but shouldn't bother the motor if its in fair shape .
Sounds to me that you might over gear your truck to the point that you'll loose performance.
What's the over drive ratio on your Tremec
John
