Hi all, new to the forum. I just got a new-to-me Sonoma a couple weeks ago. It’s a 4.3 4X4 crew cab ZR5 with 136k. I’m having an issue with the driveline. Between 1300 and 2000 rpm I’m getting a repeating 200-500 rpm surge when maintaining speed or mild acceleration. This happens at most any speed that I’ve noticed matches that rpm range (45-70 mph). I haven’t noticed it below 40 ish and haven’t driven faster than 80ish. The tach will gain for about a second then lose for about a second and continue this pattern till I have to decelerate or it’s no longer in the rpm range. I tried driving in 3 and it didn’t seem to make a difference. The CEL is not on. It’s an often but intermittent problem. Sometimes it doesn’t happen, but when it does happen, it’s just about constant. it almost seems like a dice roll at start-up. Other than that, it runs very smoothly. Any help or insight on where to start or how to fix this would be greatly appreciated. Thanks in advance!