I have a similar issue. I have a 2004 Av 2500. I replaced the OEM mirrors (with all options: turn signals in glass, power mirror adjustments, defrost, power folding, memory, puddle lights, and auto-darkening) with Tow Mirrors from 1A Auto, link below.
https://www.1aauto.com/chevy-gmc-cadillac-mirror-set-trail-ridge-tr00066/i/1amrp01765
The Tow Mirrors have turn signals on the front / side of the housing instead of in the glass, manual folding, defrost, reverse lights, and clearance lights. I know I'm losing the power folding, puddle light, and auto-darkening functions. The turn signals, power mirror adjustment, defrost, and memory should transfer over directly, but I'm struggling with the clearance and reverse lights.
The tow mirrors come plug and play for this year/make/model, except for the two hot wires for the Clearance and Reverse Lights. They provided wires and plugs, but I'm not sure where to tie them in. The clearance light should come on with the headlights. I know there are the two fuse boxes by my left foot, and I know there is a reverse light wire behind the stereo (where I tied in the rear view camera). But I'm trying to figure out the best place to tie in.
I'd love to salvage the puddle lights somehow, maybe have the reverse lights in the mirror come on with either the reverse light or the puddle light? I don't know if that's possible without causing a ton of other issues . . .