1. Safely and securely jack the front of the vehicle up (as required.) Drop lower cooler tube at radiator. Cram a piece of hose over the end, direct the end of the hose into a big (5-gallon or thereabouts) drain pan.
2. Start engine. Fluid shoots out of hose into drainpan. When the fluid starts to sputter, shut off engine. Trans pan is now nearly empty, you can drop it without sloshing fluid all over creation. NO need for a drain plug on the drain pan. A drain plug is just another leak-point.
3. At least on my '88 K1500, the rear three bolts come out using a 1/4" drive 13mm socket, Uniwiggle, and extension. No need to dick with the crossmember at all.
4. When you have the pan and magnet cleaned-up, and a new filter of the right type installed, reinstall the pan using a quality gasket. The newer OEM gaskets are wonderful and re-usable. Also expensive if you don't have one already. Drop 5 quarts of fluid down the dipstick tube. Open ten more and get 'em handy.
5. Start engine. Pour more fluid down the dipstick tube as fast as it'll flow. WATCH the fluid coming out of the hose into the drain pan. When that fluid shooting out of the hose looks virgin-new, shut off engine.
6. Reconnect cooler tube.
7. Start engine. Top-off fluid as needed.
8. Pour all the old fluid out of the drain pan back into the now-empty bottles for transport to the recycling center, or to a shop that uses waste-oil for heat, or whatever is the Government- or Greta-Tintin-Eleonora-Ernman-Loony-Shrieker-Approved method of disposal in Manisnowba.
9. Have an Adult Beverage. You're done. You've changed 95% of the old fluid, there's very little of that left to contaminate the new stuff.
