ol' fart looking to buy an old truck

Howdy all!! A question for the guru's. the last truck I owned was a 2000, so alot has changed since then. I like a detroit but I love a CAT!!!! Need some info on drive trains. I have found a 2006 frightliner columbia, it is an old iwx truck. 435 cat, fro-16210c 10 speed, with 3.25 rears. the frame has 1.2 million miles on it. inframe on the cat approx 300k ago at a cat shop with papers to document. maint history available. I am wanting to know the good bad and ugly opinions on this set up. Thanks in advance!!!!

 

I prefer a 13 speed myself. but for the price i can live with a 10 for a while. with a good core i can get a reman 13 for around $3000. thatsw what i plan if i get this truck is to swap it out with a 13 geared to match the 3.25s

 

bump

 

I guess I should have put this in the original post. I am going to be hauling containers with in a 300 mile radius of memphis, tn. weights are going to be 30k lbs and less. 1 or 2 loads a week will be heavy. There are no real "hills" in that radius were I will need alot of pulling power. I am not a speed demon, (anymore lol) i have had my 3 digit trucks. Speed is not an issue for me as long as the truck will cruise at 65. I am mainly after fuel mileage. As I stated earlier if I get this truck and run it for a short while, I can then get a 13 speed that is geared to match up with the 3.25 rears. Then I would be able to split it on the few ant hills there are around here. Thanks again for everyone's input.