Tranny lag when hot

My transmision started lagging between gears a few thousand miles ago, so i replaced the tranny fluid. The problem got fixed and the old fluid was in pretty bad shape, there as very little metal shavings in the filter and the magnet so i assumed tranny discs were good but fluid was bad. ok, now i'm having the same trouble only when the car warms up, i'm assuming i only removed maybe half of the tranny fluid and now the new fuid mixed with the old one and it doest lubricate good when it's hot.

You can buy an after market transmission cooler used for towing which might help. I had a 1997 Ford F-150 and it always shifted bad when it was over 80 degrees. I cleaned the valve body and changed solenoid pack. I found out the ford coolers were plugged which caused the problem. You could try blowing out your transmission cooler.