Two weeks ago, I took a trip to a nearby airport.  They have the cheapest gas around, so I always fill the tanks there.  The operator put in about 15 gallons in the left tank, when the truck ran out.  I left to do some business, and he refilled the truck and finished filling my plane sometime after.  I returned to the airport a few hours later, paid for the 51 gallons, and left. On departure, after climbing a few hundred feet, I noticed a definite decrease in power.  I was still able to cli