Don't worry about dropping a cylinder, it "sounds" like a maintenance thing more than anything else. So here comes the questions...
When'* the last time you changed your Tranny Fluid? If you've got mucky tranny fluid than it would over-work the engine. It sounds like at low-RPMs in different gears you're having problems. On a simple check it will sometimes look good, and still have a ton of muck.
How about Spark Plugs and Wires? Especially on forced-induction applications if you have the plugs or wires go bad then it'll be a biyotch on the low end. Even if yours isn't supercharged, and it'* been a while, change it.
Are all of your accessories working? If one of them starts to lock up or die then that'll put added stress on the engine and slow it down.
How about that thare air-filter of yours? They turn from engine friendly to intake restriction faster than some people like.