has anyone had the gears swapped? How much does this cost? Parts only cost? Thinking of just having the 4.10's with carrier swpped out with a 3.54.

 

Shop around the performance and off road guys like Randy's Ring and Pinion for a good deal. The Dana is a common configuration and parts are readily available. I would expect to pay $150 for a matched ring and pinon on a sale, and around $300 regularly.

Since you are going to have to pull everything anyway, just swap them instead of trying to install a new third member and then have to do all the bearing set-up from scratch. You will still have to adjust the carrier bearings, but it will be by thousands instead of tenths of an inch.