I have an old Chevy truck, 4X4, NP203 (full time 4X4) and I was wondering what type of RPM's I'm doing at 70mph on the interstate. It's a 1977 Bonanza with a 400ci and TH400 tranny. The carb is an Edelbrock with either 600 or 650cfm and I think it is a Q-jet and has the performer intake. It has 3.08's and stock sized Dunlop tires, about the normal size it would have come with from the factory. I've had the needle buried way past 100mph. If I had to guess, it probably tops out around 115-120mph. It can really move with that 175HP 400ci V8. I'm assuming my best possible gas mileage is at 50mph with the 3 speed tranny, but I'm curious what type of RPM's I'm running at Interstate speeds. The truck is basically original, aside from the electronic choke edelbrock carb and intake manifold, both put on back in 1992. Vehicle has just over 95,000 miles now. Any other info needed let me know. There's no RPM gauge in the dash.