I'm using 3pv with t-fhss receivers. I have come across mt-4 airtronics.(almost brand new.) Would this be a upgrade? Thanks for any thoughts on this

I would not bother. Do Sanwa Mt-44 or M12rs, or even the higher end Futabas. I have all of those new, if interested PM me.

1 step upgrade. But i would try look for mt4s or mts. Best would be mt44

As above, the MT4S would be great if you can find one, it has the same response speed as MT44 and M12S / RS.

The new MT-S is a good bet too, and if you're using standard digital servos, in SHR mode it's as fast as the others. Easily the best value midrange radio.
MT4S and MT44 are quicker in SSR mode if you have Sanwa SRG/PGS servos.