Nuvi to 2595 data transfer?

No idea what you mean by the "old way" but

Can same current.gpx be used on different nuvi models?

by the old way was taking the current.gpx and renaming it to current1.gpx and transferring it over to the new unit

Try renaming it to temp.gpx instead. That's the name Garmin's software (MapSource/BaseCamp/etc) uses.

Nope not doing it

It's possible the current.gpx file from your old unit is corrupt. Have you tried opening it with a Garmin or other program?

yes I did and it works in the 200 series units with no problems

In that case I can only suggest a suck'n'spit--that is using whatever program you prefer to read everything from your old unit, connect the new one, and then write it. In theory that's the same as manually copying the current.gpx file.