My '97 Civic EX just got out of the shop after having a new oil pan gasket (to fix an oil leak), plugs and fuel filter. Gas mileage is so-so (what can expect with 291k mi on it?), but still much better than my GF's '03 Accord V6.

Problem is still the same as before it went into the shop: when I first get in my car and drive it from startup, after about 30-45sec it lurches/shakes a little and slows down. The RPMs stay the same and there's no real difference in the engine noise (no sputtering/revving). If I let off of the gas pedal for a sec then press back down OR if I press down harder on the gas, it runs fine and will run fine for the duration of the drive. If I come back to my car after it's been off (i.e. drive to the store, go in and come back to my car and start it back up), it does the same thing. It's always at 30sec or so after the startup that it happens; doesn't happen again for the duration of the trip.
It can happen if I'm driving in my neighborhood in a lower gear or 55-65mph when I get on the highway from work.

Another thread here described the same problem and it was resolved with a fuel filter replacement. That didn't work in my case. Could it be the fuel line or fuel PUMP?
Thanks!