It seems to me, that my truck is turning around 2200 or so, at 50 mph. I have 7.50x17 tires, which are pretty tall. I also seem to remember that the standard oil "troughs" are good for about 3000 rpm, after which the puddle doesn't have time to reform. Our friends at Chev have thought of this though, that's what the sprayer things are for. I know people use to race the so called splash oilers up to 6000 rpm. I think though, that might be a little excessive. If your engine is in good shape, I don't see why you couldn't run at 55 mph all day long. But, I think your mileage might suffer. My truck does really well (milage-wise) at about 30 mph.
There is a rpm calculator at Randy's Ring and Pinion website, that you can use to calculate your various rpms at different speeds, and with different tire sizes.
Even if you have a full pressure 235, they really aren't designed, IMHO, to run at high rpms, without consequences. My old Pontiac is full pressure, and it doesn't really like to go much faster than 50 mph.
I think to go really fast all day you might want to change the gears out. But, the thing to remember is, you can only stop as fast as your tires will hold. If your drums will lock up all four, you really can't do better than that. Oops! I'm wandering again.
