Tug in 4th gear.
 

Driving home from work today I had some trouble. I'm in 4th, doing about 45, the motor boggs down a bit (as normal) and I start to feel a tug or shudder. If I let off it goes away. It happened again a couple of miles down the road and I downshifted to 3rd and it was fine. I checked my tranny fluid when I got home and it's ok. I haven't noticed if my rpm's are dropping when it shudders.... I haven't changed my fuel filter yet, but it feels like a tranny issue. It's also ok under hard acceleration. Any thoughts?

When were the normal tune up items done?
PCV
Fuel Filter (you said not yet?)
Plugs
Wires

Any other symptoms?

I haven't done any of the above... I was planning on plugs and wires at NEBF just didn't get that far. If it's engine performance, I'd see a drop in rpm's right? My tranny is a GM reman done before I got the car.

Actually once the torque converter locks in you feel any ignition issues or oddities that exist.

I'd be inclined to start with the tune up items, since you probably want them done before winter.

Aaron found a huge difference by changing plugs and wires.