Time goes faster the weaker the gravitational field you are in as long as your velocity is constant. The Voyager probes have moved a long way from the sun and its planets so I presume time must be going slowly faster for them. Is this true and if so do we know how much faster time is going for them than Earth?
You can see this answer for the formulae. We would expect that Voyager 1's local time is faster than Earth time by about one part in one hundred million.
I don't think that the Voyager oscillator is stable enough to measure that small of a difference. So we can't directly answer "is this true". However it would be a mind-blowing discovery throwing our most basic understanding of physics into disarray if it weren't true.