another carrier bearing Q

[D-Rat]

what are signs of it going bad aside from obvious driveline vibes? Dang truck is too low for me to get under it easily....haha

Am getting some vibration under the truck, and I feel the truck doing the opposite of surging on the freeway...like the brakes are being tapped intermittently almost, and I'm wondering if there could be enough rotational resistance in the carrier bearing to get this feeling, or if the issue is engine related. In other words I can't tell if it's running rough or if the issue is further down the drivetrain. The truck is idling good, has no vacuum leaks that I can find, and the ignition system seems to be in good shape with nearly new wires and HEI. I don't really feel this at lower speeds.

strange thing to ask, I know, but I'm having trouble diagnosing exactly what's happening here