well, That does seem pretty high for an 01 without any warranty -- but I bet he gets that for it...
I'd say keep yours and mod the heck out of it just to stay outta debt and start modding faster!
as far as power -- all the 7.3's are close to the same... but you will be more sluggish with the dually and 4:10 gear ratio (not to mention worse mileage)