Mobil is not the right viscosity, it has cSt@100 7.2, while OE ATF is 7.5 and has a better friction additives package. Shifts with Mobil are more harsh. You may try to cure it with HFM since you've got two boxes...
Installing additional oil cooler is a very basic job. Get Hayden Rapid-Cool of your choice and aluminium angles and bolts/nuts in Home Depot. Here's my frame for the cooler that mounts onto A/C radiator (it has mount holes):

And that's how it looks on the car:

Wise to install a 3/8" Magnefine inline transmission filter at the same time.