So this isn't really a question or a statement, it's more of a thought process. I've already thought it out and read it so I know at least part of the answer for me, but given that the 31" tall tire is factory, and even my tires which are a bit wider than factory and still the same height so perhaps this information will help someone else, or maybe you'll disagree with my thought process and share yours.
So this is a speed / RPM chart for the various common ratios, or at least the ones that concern me atm.
Current gears at 3.41's so I'll start with that one. Mainly we are concerned with direct drive but I have included 2nd gear to see the RPM change at speed for a downshift like getting slowed down climbing a hill. Anyhow.
3.41
65MPH - 3RD 2,400 RPM
60MPH - 3RD 2,200 RPM
55MPH - 3RD 2,000 RPM
60MPH - 2ND 3,600 RPM
55MPH - 2ND 3,300 RPM
3.73 (the ratio my differential has in it)
65MPH - 3RD 2,650RPM
60MPH - 3RD 2,450RPM
55MPH - 3RD 2,250RPM
55MPH - 2ND 3,600RPM
4.10
65MPH - 3RD 2,900RPM
60MPH - 3RD 2,650RPM
55MPH - 3RD 2,450RPM
50MPH - 3RD 2,200RPM
50MPH - 2ND 3,600RPM
4.56
65MPH - 3RD 3,200RPM
60MPH - 3RD 2,900RPM
55MPH - 3RD 2,700RPM
50MPH - 3RD 2,500RPM
45MPH - 3RD 2,250RPM
45MPH - 2ND 3,600RPM
Ok so it's easy for me to see from this chart that keeping the 3.73's are out. It's not enough. As ya'll already know no matter what I choose everything is a compromise. I kind of feel like the cruising RPM in third towing should be at bare minimum 2,500RPM. And not over 3K. Not saying that the engine wouldn't run along happily at 3,500 but I sort of feel like that's great for a hill climb but not really necessary at other times. 4,10's put me in this range for towing at around 60 - 65mph (speed limit for towing on the highways around here is 60mph or lower in some cases.) 4.56's are pretty much going to cap me at 60mph, though I could do 65, 4.10's would allow 70. It's all a compromise. With the hills around here 4.56's look real attractive for towing.
Now I'm going to throw in my second but not quite as big of a concern. Running empty in overdrive.
3.41
80MPH - OD 2,050RPM
75MPH - OD 1,900RPM
70MPH - OD 1,700RPM
3.73
80MPH - OD 2,250RPM
75MPH - OD 2,100RPM
70MPH - OD 1,950RPM
4.10
80MPH - OD 2,450RPM
75MPH - OD 2,300RPM
70MPH - OD 2,150RPM
4.56
80MPH - OD 2,750RPM
75MPH - OD 2,600RPM
70MPH - OD 2,400RPM
When running empty and looking at that it's no wonder why the engine likes to run at 80mph or higher on the highway! Even though I like to run at 75!
I can see why 4.10's are kind of considered the gold standard in these trucks. No not as good a towing gear as 4.56's but not as limiting in direct drive either. I honestly don't think 4.10s will hurt my empty freeway mileage much if at all, but 4.56's certainly will. If I still had the bird farm and was running all over the state for feed I'd go with the 4.56's, but now.... I just really don't know how much towing I'd do and if it would make the 4.56's worthwhile or if they'd just become a PIA. I think because of the 700R4's low first gear that I don't think I'd have to worry to much about it short shifting 1 - 2 even with 4.56's so there is that. Although delayed a couple years now I still plan to replace the 305 with a 350.
So I will probably order parts on Monday, that gives me until then to decide if I'm going to go with 4.10's or 4.56's. I think I'm leaning towards 4.10's
