OK, I'm back from my run, where I do my "best" out-of-the–box thinking, and I have a couple of basic questions for the OP:

1) Are you saying they appear to get darker during the fixing?

2) How do you know the prints are getting darker? Are you using IR goggles? My prints always appear darker in my fix than they do in the developer. Why? Because my safelight, and it is a good, bright one, is closer to the developing tray by at least six feet, than the fixing tray. I simply cannot judge them effectively until I turn on the lights.

3) You say you changed developer. Is it possible you are trying to print, same paper, with the same exposure as with the first developer, and are expecting the same result?

130 is faster than Dektol and at least as contrasty, but I don't know about Neutol.

Just throwin' it out there.