Disconnect the cooler line, pump and fill as you go. I can't count the amount of time I have done it on my trucks. It is easy on the GM HD stuff. Pump a quart or two at time fill and repeat until clean.An ATF exchange is a bit beyond what an shade tree mechanic can do. This typically requires disconnecting the ATF cooler lines and hooking them up to a machine. The pump in the transmission is used to exchange the old for the new.
$80 an hour!?!?!!! Around these parts the hourly rate is about $150.
I have a 2017 3500HD. I did all of the minus the plugs and wires at like 38,000 miles. I am now at 42,500.
I will probably do the plugs and wires at around 60,000. I
I did replace the transmission pan with a PML 6L90E deep pan which has a drain plug unlike the stock pan.
It is nice because every other oil change I can do a drain and fill. The deep pan uses the stock filter and holds about
3 more quarts. Big reason why I did that was is this truck just tows. I have my travel trailer, boat, and the Submarine Veterans parade float.
It also good as GM recommends the service on the transfer case and 6L90E every 45,000 miles. I think the lack of people doing that kills them early.
I have to ask why Amsoil? The Dex VI is the proper fluid for the Transmission and Transfer case. I don't mess around with that. GM DEX VI or I wait until I can find it. I don't like putting anything else in those items, but I digress, I think the best thing is keeping the fluid in those cleaned and serviced every 45,000 miles.
That isn't a bad price for all that stuff. I found the biggest pain to be the coolant and getting all the air out. The rest of the stuff is pretty straight forward, but I have a nice garage and all the tools to do it.
I had the dealer do the first transmission service on the Caprice 6L80E, fluid exchange and I sat with the guy and chatted about the cam install while he was doing it. I told him I would leave, he said he liked the company. Took about 2 hours. The Caprice is difficult to do with no dipstick and the car has to be perfectly level to check the fluid out of a weep hole. Took longer for the tech to get lines off and on than anything else. It cost about 100 bucks more for the dealer to complete the service then if I had done it at home, so at the time it was worth it to me. I have since added a dipstick, Camaro Deep pan and CTS-V wide mouth filter. Now I can do it myself at home.