Groove means a lot of things, and can be different for people. For what I've heard it has to have some kind of rhythmic flow and regularity in the ACCENTS of the notes. If those accents doesn't pop out like they used to, I e when you lean in with your fingers to produce ONE louder note at a certain point in comparison to the others, it can be quite hard to determine the culprit. I know for one, that when I have a compressor on my groove and accents suffers badly. So I eschew compressors to allow the dynamics to happen. The "punchiness" of different pickups output that gives you a percussive thud to each note can be crucial.
QUESTION:
1. The groove, that YOU are stating, is it when you do fingering, or when ju do pop, thumb, and slapping the bass, or both? It can be very different then, in terms of groove. It can be both. A groove can be kept regardless of fingerstyle playing, or pop-thumb-slap playing.
I have a friend who owns a regular stock Squier J-bass. I have much easier time playing grooves on that one, regardless of that the strings and action are the same. For one thing, one tends to play more grace notes before the real notes should be played. And it's easier to keep tempo on the grooves.My grooves just floats on that one, more so than any of my other basses, of one which is a Dingwall, no less. It just lends itself to that more on my all other basses. He says this too, comparing all his other basses, this is the one. It's just that that bass probably was a fluke, since he went through 7-8 of them in the same store, before he stumbled up on this one. Some basses just invites or induces a style of playing of yours that you can't do on any other bass. Well you can, but you have to lean in and hone it too much. Woodshed. We still have no clue of why, in spite both of us scrutinizing the thing. At least 2 times a year (ongoing for 10 years now) I ask him to sell it to me, when I have the suspicion he's in a financial predicament. The answer's always no.
The reason I say this, is because the first post suggests that you actually could groove on your old bass. The groove is a problem on the new bass ONLY isn't it?
So if you could groove on your old bass, you certainly have no problem on the actual musical side of it at all, say, playing in pocket, with a drummer, in time, general flow, and so on. So I think it's a problem with bringing the new bass into the same comfort zone. Trust it! DARE TO MAKE MISTAKES AND NOT BE MAD ABOUT THEM. Only then you'll know.