I just turned over 13,000 miles in my 235-54 truck with a .72 T5, 3.42 Camaro (62") diff and 28" tall rear tires. My cruise speed is 70 mph @ 2000 rpms and the truck is on the road every week.
I'd suggest you check out my WEBSHOTS albums: "Shoebox and Tips and tricks" that goes into detail about the conversion. One thing I might add is that if you wanted a lower cruise speed you could retain the 3.90 R&P in the stock 54. This would put you a little deeper into the torque/power curve at a lower ground speed which would improve the overall efficiency of your engine. Some of the folks that have made the R&P chunk modification can fill you in on the details. Feel free to PM if you have any questions.
Dave
