Tranny Flush

When I picked my truck up from the shop the other day, the manger said that he noticed I was about to change the transmission fluid (he saw the fluid and filter on the back seat). He said to leave 20 - 30% of the old fluid in there and replace the other 70 - 80% with new fluid. I asked him what about the filter inside the pan, and he said that he never changes it unless the gasket starts to leak and he has to pull the pan off anyway.

Truck has 100,000 miles, this will be the second transmission fluid change (first one at 50,000 miles - changed 100% of fluid).

I dont like the sound of only replacing part of the fluid and not changing the filter, but this guy is the highest level technition, and is also the owner/manager so he knows his stuff, but he also might be try to sell me his tranny flush service.

What do yall think, change all the fluid, or do it like he said?

anytime ive done a tranny flush ive replaced everything all the fluid, filter, ect...

I've heard of this before too, but never done one like that. I think this recomended when it's getting alot of miles and never been changed. Since it's only 50k on the fluid, I would do it all.