JCVQPWR

I have a 97 Pathfinder SE Auto 4x4 with 240K miles. Rebuilt tranny at 180K miles. I've had the SES light for a while and had it checked out today, and the code it threw was P0501 which is VSS Range/Performance. Does this mean to replace it? Because the P0500 light is VSS Malfunction. The next problem I have is with the ATP and OD OFF light. During start-up, the OD OFF light would blink a few times. I'm not sure if the ATP light is related to the OD OFF light, but when I leave the transmission in Park, the ATP light would turn on, but turns off once I move it into Drive or any other position. The last and final problem only happens at around 50+ MPH. Say merging in a freeway going 50 or so MPH, when you give it gas to downshift into 2nd or 3rd gear, instead the engine revs as if in neutral. I'm thinking this problem is related to the ATP light. A mechanic told me that the ATP light is on because the Park/Neutral Switch is not activating. Someone please give me some insight. Thanks.

Forgot to mention the tranny was rebuilt @ 170K. I don't have a CEL, its the "Service Engine Soon" light.

I have a 97 Pathfinder with 240K miles. During start-up the "OD" light flashes, the "ATP" light shows up when put into the Park position, turns off when I move it to any position except Park. Also my "Service Engine Soon" light is on. The only problem I'm actually having is the OD not working sometimes. On the freeway at around 50-60 mph, when I give it gas to downshift to pass. The transmission just slips. Any help would be appreciated. Thanks.