IMHO you are so far into the range of 4.10 gears it's not even funny....

and, with OD off the trans is at 1 to 1 ratio converter locked. How are you coming up with "effective 4.56"? Are you talking manual second and a lockup switch??

1st: 2.45
2nd: 1.45
3rd: 1.00
4th: 0.69

I don't understand the statement....

From what I can remember, the calculation took into consideration the transmission gears, the differential gears, and the tire size to get to "effective gear ratio".

I don't recall the calculations, but the end result (IICRC) had me at a higher numerical gear ratio (lower gearing) in 4th with TQ locked and overdrive off, than if I had 4:10 gears running in OD....

I'm saying even with your mods towing an 11K trailer the combo would live a happier life with a 4.10 rear gear.

My race trailer is probably tipping in at 9K + and with some of the grades in the desert sw, I wish I had my 4.10 gears back. I swapped them out as the truck was basically our "station wagon" for many years and it became much nicer to drive with the lower rpm. Now that we have multiple cars the truck is pretty much set on "tow duty" and with the addition of a larger trailer, I'm now wishing I had the 4.10 back.

you stated that you slow down to "40mph" on some grades.... what rpm are you turning? Thinking out loud that seems quite low so that's why I'm thinking 4.10 gears would get the job done in a better fashion. I know on the steeps my combo, as many do, is happy at 2200 rpm. good balance between maintaining power and keeping egt in check.

This is very useful perspective...thanks!

I'm considering 4:10's now. As I've said earlier in this thread, I love my tall gears on the hwy when not towing, but the truck is used primarily as my tow vehicle. I have no doubt it would do much better in any gear up a grade when towing if lower gears were installed.

My ONLY concern is the cab noise and my "mechanical sympathy" for the engine at 2200 rpm on the hwy. As you said, it's just more comfortable at lower rpms.

I have the advantage of having the help of my brother in law, a formally trained diesel/heavy truck mechanic. He thinks we can bust it out in a day. I don't care how long it takes, if I can do it for ~ $500 or less, it probably makes sense. However, before I do anything, I gotta tow with the new mods to be able to see what effect those have had.

I'm off for some internet shopping for gears.....

With my setup I am sitting at around 19000 lbs with my trailer with 3.45 and 315 tires and live in mountain style terrain. With a six speed its not bad and even better on flat land as you said 70 @ 1500 makes a quieter truck

I suspect that you have more going for you with all the mods you list, the closer ratio gear splits, and additional gears. Man would I love a six speed. Your taller tires offset that a bit though too...

Prior to J Body's discussion and perspective from someone who's experienced both ratios while pulling, I had pretty much concluded that my best set up is the 3:55's in service now, as I could run in 4th with OD locked out when pulling grades, and still have OD for the flats. After his description, once again I'm not so sure, and it sounds like I'd only have to get used to a bit more in-cab noise and less top end speed on the flats if I switched out to 4:10's...

I think that I had calculated with 4:10's an rpm at ~60 mph of 1900 to 2100 IIRC. While that's not terrible, it is a bunch more noise than at 1600 - 1700 rpm.