I'm running a SM465/ 4.10's/ 33's on my K20. It is a good towing setup for a non-OD rig. It has plenty of power, I don't use granny. I run about 3K RPM at 70 MPH, give or take. Around 55-60 seems to be the sweet spot for my combo. It's also nice around town. I ran with 31's too, and definately prefer the 33's. Unloaded, on the interstate, the R's get to be a bit much, but I'm used to OD rigs. I don't like to run above 3K for long periods of time. It keeps pulling well over the legal limit, though. Since it's my DD, I plan on stepping up to 35's whenever I get the chance.