45rfe transmission feels like it's slipping at low rpms

My transmission was rebuilt about 4 months ago
and have had no problems since until I felt a light
thump in trans while going to my doctor one day.
There's was no problem that day. But I noticed it
was a half quart low on fluid I added fluid and no
problems. After a few weeks which is now it is
starting to feel like it's slipping in low rpms all
gears except first but if I g8ve it a good mount of
throttle it will cycle all four gears no problem then
ride just fine but as soon as the rpms drop it's back
to shuddering or slipping but I have had all
electronics inside trans replaced or so I was told I
know for sure the solenoid pack was changed and
new seals were installed but the exterior sensors
still look old or original.i don't want to have to put it
back into the shop for 2 +weeks again.