Just get the exhaust manifolds, turbo and intake manifolds from a 6.5L turbo. They bolt right up. You will gain a lot of power and be happy. You will need to turn the fuel up in the pump, too.
You have the old DB2 mechanical pump - be happy. You have not PMD/FSD to fail which is THE most common failure on the old Detroit 6.2/6.5s. Put the turbo stuff on and you will change your mind about regearing. I owned a 1995 Suburban 6.5L with 3.73s and it was too much gear for me...keep in mind my car hauler empty is 4400lbs and I towed two cars with my burb many times. The MPG is also low for those gears. I got 20mpg with mine - you should be near 27mpg or so. May need a new set of injectors. If you swap these go with some turbo or marine injectors.