Rear end replacement price.

Are you still with Mercer?

 

I just had my 3.7 Eaton rears replaced by a shop in Utah with 3.25 on a 2000 Pete 379. Replaced all the axle seals while in there, and cost me $4,200 for rebuits.

 

Re-gearing won't be cheap, the heavier the rears the more they will cost. Are they Mack rears?

I have 46K rears, last November a new center section for the front axle was a little over $4000, no labor included.

 

Oscar is right, the heavy rears are more pricey, you're looking at 7-8K in parts but over 2-3 years it'll pay itself back in multiples with MPG savings.
If I were you, look at going 3.08 on the ratio. It'll still pull fine but you'll downsped on the highway and get much better MPG.

 

I would normally say to call wreckers and ask about a trade but normally heavy rears get heavy gears. not too many guys spec 46k with 336. but it may be worth a shot, maybe a wrecker will trade your 46 banjo and carriers for a light spec one if you pay them a little difference and maybe get them to do the swap over.