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Dean,
You are correct. We have somewhat similar setups. I will share a bit of my history with the trucks. We started with a PSD 250 2WD. It was a 7.3 with the auto tranny. The 250 was simply not heavy duty enough to deal with the trailer. It pulled the trailer with no problem. The problems were the sag when hooked up to trailer and the multiple transmissions I had to have. I ended up replacing the transmission 3 times. Thankfully all were under the warranty.
In regards to the transmission I try to use cruise control anytime I can. In the 250 the least little uphill bump would cause the tranny to start "searching" for the proper gearing. Of course I would have to take it immediately off of cruise. So I ended up not using the cruise control much of the time. The sag problem was more problematic and I never ended up solving it. I would have had to install air bags or stronger stiffer shocks.
I believe the 450PSD has solved both problems listed above. The sag was solved because the truck is simply very stiff with much heavier duty frame and springs. It also sits at least 4 inches higher than the 250. The cruise control and tranny problem was solved with the 4.88 gearing. The cruise control now works almost to a fault. It will not kick down to the lower gearing until we are in a rather steep hill.
The 450 has exactly the same engine and tranny as the 250.
I was very worried about the 4.88 rear end and had to be talked into getting it because of my brother. He is very mechanically inclined and I trust his judgement in these types of issues. I'm sure I get less fuel mileage because of the gearing but it is almost negligible the way I use the rig. I simply remember that I got the truck for TOWING not for fuel mileage. Of course with the cost of fuel going the way it has we're rethinking the whole RVing thing. Not yet to the point of actually thinking of stopping but certainly one or our long range options.
My rpms show about 22.5 k towing at about 62 - 64 mph. If I had the 3.73 I'd probably be about 17 - 19 k. So of course I'd be getting slightly better mileage.
I wish I'd gotten the 4WD but it was not on the rig I was dealing on. If we ever get another one it will have the 4wd. Not that I'd use it much but there have been a few times it would have made a difference.
What I really want is a HD class 8! Now there is a tow vehicle.
I was pleasantly surprised that the 250 and the 450 got about the same fuel mileage. My best estimate is that I'm getting between 10 and 11 miles per gallon with the 450. We don't have the onboard computer so this is all hand calc.
There was a fellow at the Quartzsite gathering this past January that had a 2007 450PSD. Wow! Was it nice. He had only had it a few months so was still getting used to it. It had all the bells and whistles on it. He was very satisfied with it so far.
Dennis
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