EFI - electronic fuel injection, which meant a big thing back in the mid 80s.
Perhaps new fuel injectors are needed?
A proper fuel injection service requires more than pouring some sort of cleaner in the gas tank, after all those years it might be hopelessly clogged.
Might be time for an engine rebuild or swap as a worst case scenario.
Before you do - look into the transmission, see if that might be causing any issues.
Small oil leak may be the oil pan gasket or the pan itself.
Have you had the car looked thoroughly with a mechanic to find other possible problems?