Rear ends and transmission compatabilities

Calling the experts! My problem...when loaded, mid to heavy....my truck is TERRIBLE starting off, and #### near impossible on a hill without stalling. Trying to slide tandems back when heavy, usually stalls out or just rocks the hell out the truck! Surprised I have been able to maintain my driveline for 2.5 years I've owned it.
The truck, 2005 Classic XL. DDEC V 14L. Originally had an auto shift, 10 speed replacement prior to my purchase.
Trans tag is trashed, not readable. So no specifics there.
According to tag, 3:21 rears.
70 mph about 1450 rpm.
22.5 low pro tires.
I've considered going to a 15 or 18 speed. 13 would do nothing for my low side problem.
Any advice or thoughts?

 

A 13 isn’t gonna help you in the low side. The B series 18 has the lowest low hole. The A series 18 is rare but they are out there, it will have a lot higher low hole with both ending at .73 unless you wanna talk about the RTLO15618B. First design and trash in my opinion. The RTO 15715 is your next choice for a proper low hole to get 3.21’s started. And with only 20 Percy overdrive be about right in the big hole too on low pro 22’s. Now I haven’t done the math I’m just shooting from the hip. I had a truck with a 15 over, 3:25’s and low pro 24’s. It had a CAT but it done really well.


I know a guy that likes to run 3.08 rears, tall rubber and a RTO14613 with a .87 final gear. By the math it supposed to run out almost identical to 3.55’s and .73. But he struggles with it, they break a lot of driveline/gear related parts.

 

Do you know, is an 18 a direct fit or need driveshaft work?

 

If it’s a super 10 possibly to make it work. If it’s a straight 10 you’ll have to shorten it

 

First go here, this is a complete spec catalog for Eaton transmissions.

https://www.eaton.com/content/dam/e...transmission-specifications-catalog-en-us.pdf

Second, the average 10 I have found has a low of ~12.8, some have 14.4 or 14.7 but that seems to be rare.

However, the 18 has a low of 14.4 or 14.7. Some 13 speeds are just 18s without the low O/D option.

Wore out mentioned the difference between A and B, they are 14.4 for A and 14.71

The catalog has the sizes so you can see what will fit.

It doesn't cost much for a driveshaft to be fitted, I paid $350 the last time I had it done in July.

 

It would definitely be helpful if I knew more about mine. That tag is just destroyed. What do those numbers mean? 12.8, 14.4, ......
Are you saying a 13 would probably just fine to fix my low gear issue?