Rep Power: 0

09 Civic 4 cylinder, about 135k. Driving in fair weather, moderate inclines at most. When accelerating hard (or at least, about as hard as this car can, 5ish k rpm, not in the red, but trying to get up to a merging speed), as the car passes through the 50-60 mph range, there is a secondary vibration. About every three seconds there's a half-second something vibrating other than the steady vibration of the vehicle. Maybe a slight change of power, but if so, very slight, barely noticeable. Maybe a burning smell but the smell has only happened once or twice. Does not happen if slowly accelerating (lower RPM but same speed range).

Have religiously followed maintenance schedule, transmission fluid changed around 100k.

Is this early warning of transmission slippage/damage? Or possibly something else?

Car needs shocks, tires, and motor mounts (and heck an alignment) and I don't want to put too much into it if it's going downhill. On the other hand, if there is something I can do to prevent things from worsening and up my odds of getting to 160k or 200k, I'd like to know.

Thanks in advance.

 
Rep Power: 221

Motor mounts could potentially be part of that vibration.