Truck towing question

the cummins will always be in a 3/4 or larger.
all depends on how many miles you drive it (DD?) and what ya pay for gas/fuel. the 12 valve cummins is 1,000,000 mi engine, but it will need fuel system rebuild well h\before that. I've had several d22 and 300 late 80's. early 90's cummins. bought 85 cummins 300 new, still got.
I personally always prefer a d200 for towing anything. heavier frame, brakes, everything pretty much.... slant will pull more thasn ya think on level to gently rollon roads, once it gets rollin!! LOL like they said, the older trucks were lower geared.
good part is your in Ca!!!!! no or little rust. get good pretty much staright body, and go from there!!
in most places expect to pay good bit more for a cummins truck.
sidenote. I just got my property tax bill. somehow they had my 95 d300 cummins on there twice, once as diesel and then as gas truck. (how!????). the taxes on the diesel were 3X that for gas!! LOL friggin 20 years old truck!! too!