after reading through this, I also would not be all that worried about power over the rockies. You will slow down, sure, but most of the time you should be able to easily keep up.
In my 1981 240 4-speed I used to own, I welded a receiver hitch onto it, loaded up three grown men and a cooler of food and drinks, picked up a tow dolly, and towed a 1981 VW rabbit half way across the country with the 240. The rabbit was also loaded with moving boxes.
the only time I ever had a problem was getting through NYC with the car in tow with out destroying the 240. Blew out two of the side shift seals, but that did not happen until somewhere in IL, and because we were going about 75 with the rabbit on there. Most of the trip, the 240 did 65 with no problem.
I also later took the same car out to CA over the rockies and down part of the coast on highway one. (something I have done with several mercedes, lots of fun!) The grades dropped me to 3rd and 45-55, but she chugged right up the hill, and that was the extent of it. Made up for it on the back side.
