Grand Caravan Transmission slip

I have a 2000 Dodge Grand Caravan with 3.8L engine and 4spd auto., recently
and only when cold, it has started to slip (rpm's climb about 300 revs then
drop) when shifting from 2nd to 3rd. Then it completes the shift and runs
fine, have not a noticed slip from 1st to 2nd or 3rd to 4th. The trans
filter and fluid was done last year at a local Dodge dealer and they did put
ATF+4 in it (as stated on bill). The vehicle has 140,000km on and was bought
2 years ago second hand. Ay ideas or suggestions as to what is wrong, I
would like some input before taking it to a shop and hearing a "needs
complete rebuild" when it may just require an adjustment or something else.

TIA.

 

It needs to have a tech look for codes if any than do some diagnostics.
Larry

 

Did they put in any additives in addition to the ATF+4? Check your bill.
If yes, get it changed again but tell them no additives this time. Also
there are 2 sensors that go bad or can get bad connections or gunk on them.
Hopefully an honest dealer will check the codes for you.