Trans Flush? Always do my own.
I just warm up transmission open line from transmission to cooler add a clear hose put the hose into an empty bucket, then make ready replacement fluid, place funnel into transmission dipstick tube, start truck and fluid flows into bucket while I replace it at a good pace until fluid comes out the color of fluid I'm putting in.
1999 GMC K2500 BURBAN, NAVISTAR enhanced 6.5 td aftercooled, dual alt's, PSC p/s pump w/HD cooler, redundant FSD's, HEATH program, turbine/downpipe wrapped, 4" SS exhaust, real time OBD2 data logging w/device controller, EVANS waterless coolant @ zero (0) psi & 135 gpm pump, 4L80e w/kevlar and premium steel w/cryo treated input/output shafts running @ 100 deg. F & 140 deg F towing, all synthetic fluids, AMSOIL bypass system, MileMarker hydro, dual fuel tanks, and on and on, questions PM me.