Wife bought a toyhauler tonight. Guy said it was pretty heavy.
I thought it would be no problem for the IDI. I was wrong!
NAs mostly only good for flat road towing unless you're towing something small/light. You'll want either an 093 turbo (or PSD or gasser). Maybe an 085 or 088 would work but 093 is the best one, if you're gonna be buying a kit to install. Well, there's Banks also. But I think 093 is the most common?
My high mileage (newer IP, I think) 87 F250 NA with a 3.55 rear end was pretty slow on hills too when pulling a 27ft travel trailer. I could usually stay at 45'ish give or take since it would kick down to second gear. In SW SD on a flat highway with high cross/head winds, I had the pedal to the floor doing 50-55mph. It was shorter than many newer trailers though, so that's probably why it wasn't as bad. I hated towing a big trailer and hated it being separate from the cab, and it was too slow for cross country use, so I got rid of the trailer.
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The F250 is a snail in the mountains without towing. I never towed that trailer them, thank goodness.
So then I got my ATS 085 turbo motorhome (4.10 rear). It was similar in heavy head winds on a somewhat flat highway in KS last year. Pedal to the floor, doing about 50-55. Not much can be done about that though. It does seem better on hills. but I have to watch EGTs very closely. I can't stay at 65-70 on big hills without making EGTs awful high. It's impossible to have proper cold air intake due to van engine bay size restrictions and the ATS 095 turbo design, so that doesn't help any. I have thought about trying a
metal semi rigid clothes dryer air duct to give it some cold air. It might help the fuel economy and power of the motor, as well as make it run a bit cooler on hills.
I haven't had the motorhome in mountains yet.