transmission problems on 2005 Buick Rendezvous

transmisson shifts hard . sometimes doesnt seem to matter hot or cold sometimes 1st to sec. sometimes all gears transmission shop code reader shows nothing and auto dealership shows nothing

Asked by for the 2005 Buick Rendezvous
I had the transmission fluid changed and it has been good for about a year. It was slipping a little when starting off cold and that also improved but has started again.
SOME PEOPLE SAY USE LUCAS TRANSMISSION TREATMENT so I will try it.
3 answers
my 2003 did this and i changed transmission filter and fluid and its running much better
How is the fluid level? When was the last time you did a transmission service?