Transmission problem
1991 Lexus LS 400 V8 Two Wheel Drive Automatic 200000 miles

Hi,

My son recently purchased a 1991 lexus ls 400 with 200,000 miles on it.
the cars shifts fine in all gears, but for some reason when you kick it down to pass someone the only way it will up shift into the higher gears is if you ease up on the gas pedal.
It shifts perfect in all gears driving it normally, the fluid / filter was recently changed and toyota T 4 fluid was only added.
Any ideas on this? is this possibly a shift control solenoid? Any help would be greatly appreciated
There are no check engines lights on either.

Thanks,

Tom