Mark this is a little confusing. The negine oil does not influence transmission behaviour as it has its own oil and filter (inside the trans) and uses ATF (automatic transmission fluid).
If your trans is not shifting correctly and you have not had it serviced (oil, adjustemet and a filter clean) then it most likely needs it.
Changing your engine oil once a year is a little too long as well. 6 months with low miles or more frequently with heavier service is indicated. Check your under-bonnet stickers or efer to a manual/handbook.
Jason