Welcome to The Stovebolt. You can get a 3:55 ring and pinion gear set for your truck from Patrick's. I think mine was about $150 when I got it from him. That will reduce your RPM's with your SM420 tranny to a comfortable level allowing 65MPH cruising easily if you have the stock size tires/wheels. You may have to wait a while if he's out of stock. I can't help you with the 5 lug question but I'm sure someone else will chime in. Good luck.
