I've had 2 99 Burbs, both 5.7 vortecs. Had to change the starter frequently on the second (current)one, because of a flywheel problem. Pulled the starter off the other Burb and took it apart, hoping to swap the drive end housing. Then I found out that the first Burb had a factory style gear reduction starter, and the one I was trying to fix was the standard type. The internal parts don't interchange, but the starters themselves are interchangeable as long as the bolt spacing and nose cone length are the same. But that part is pretty much true on the older GM starters too.
The vortecs are prone to backfiring and crossfiring if the distributor cap and/or rotor get carbon tracking in them. Guess it happens on TBI engines too, but the only one I have had didn't have that issue. That's what initially happened on my current Burb, before I got it. By the time I got it in early 2013, the starter drive and flywheel had damaged teeth. If it landed on the bad spot, you'd have to bump-crank it to get it to start. We didn't drive it a lot, so just an inconvenience then.
Finally in 2016, after replacing 3 starters in as many weeks, I found a mechanic that was willing to tackle the problem. By this time, the truck had brake problems too. He replaced the flywheel, and the master cylinder and both rear wheel cylinders. After that, started and stopped like it should! Since then, I've put a Blue Streak rotor and an Accel cap, both with brass contacts. Haven't had any more trouble with carbon tracking.
Haven't personally had experience with aftermarket gear reduction starters, but I know people like them for the older trucks that have the big starter. The vortec style is a lot lighter, which is good when you have to R&R it much!
