Not sure if you mean a different sort of hold, but typically, the merchant sends a request back to the processor saying "Joe wants to buy something worth $54.04, is that ok?" But they don't have the transaction all done, so the processor just says "We have an outstanding charge of about $55 coming." When the charge finally clears, and it could be a day or few, the exact number goes on as a charge, but in the mean time, your credit line (CL) is lessened by $55.

For gasoline, usually the hold is a lot more. You purchase $60 worth of gas, and the hold could be for $100 until the transaction finally clears. For a few days, your credit line is down $100, not $60.

Restaurants can also cause this problem, to the tune of about 20%. If you eat for $50, they'll hold say $60 to cover the amount of the tip you put on the card. Even if you tip cash they'll still hold the higher amount until the transaction finally posts.

These may be the pitfalls you are running into.

You may want to find out if you can access your account online. Doing so would allow you to get a better feel for the rhythm of the cycles.

Note: complaining to the merchant that they are not processing their payments fast enough probably will get you no where.