Here is a link that will help you guys figure out which gears to run with what tire diameter and transmission. Everyone is talking speed which is only one component of this problem, making sure you have enough torque available is important as well as speed.
Take a look at the spreadsheets which are available in this thread. The file names include a number which is the diameter of the rear tire in inches from the ground to the top of the tire. If you are trying to build a truck that cruises down the freeway I normally shoot for 2000rpm at 65mph or something close to it.
My 66 GMC has a TBI 350 200hp with a 700r4 transmission, 460ft/lbs of torque to the ground, 30" tire diameter, 3:73 rear axle ratio, .70 Od ratio.
Click on the file with the proper tire diameter and the excel spreadsheet shows different engines, transmission ratios, for a given diameter. My truck is a good highway cruiser @460ft/lbs of torque but if I was pulling a trailer I would gear it differently.....or just shift down to 3rd gear 1:1 ratio and have plenty of power but have to turn higher rpms so my fuel mileage would go down.
See what you think.......hope it helps you....figure out the gearing, speed issue.......go down to posts 6 & 7 for the links...
ps see how much torque your truck currently has then try to keep the torque close to or higher than the 460ft/lbs depending on what you want the truck to do, i.e. highway cruiser or stump puller...
http://6066gmcclub.com/forum/showthread.php?t=48090
Here is a link to the 33" tire diameter spreadsheet:
http://6066gmcclub.com/forum/attachm...7&d=1395158086