My 01 automatic is doin some wired EDIT! 100k on the tranny and it's shifting back and forth at 45 mph and sometimes at 70! Sometimes it's not kicking in gear when I put it in drive so I have to shift back to neutral and back to drive. It even sometimes surges like it kicks in really hard when I'm stopped at a sign or light. My guess is the lockup but really hope it's more simple! Any ideas?

 

It could be the electronic solenoids that control the valve body. A tranny shop could do a pressure test on it and tell you for sure.