Why do my pre-cooked hams always take way longer than they should? My ham is 8.5lbs half-ham and was refridgerated, but not frozen. Here are the instructions that were with it.



Here's what I did:


Preheated the oven to 275.
Removed all packaging and put the ham face down on the pan.
Wrapped the pan in foil. This covered the ham too.


It's been baking for 3 hours (so well past the recommended 2.25 hours) and is only at 71F degrees. I've been shooting for about 140F since that's what I've seen online sites recommend. I have this problem with every ham I try to make. They all end up taking like 6-7 hours. What am I doing wrong?

I've tested with two different meat thermometers so I doubt they're in error. Also, when I leave the meat thermometer in there but not in the ham (I don't have an oven thermometer) it reads as 250F so even if the oven isn't quite at the temp it thinks it is, it doesn't seem significantly off.
Apparently the results you're getting are more or less by design. The How to Bake a Ham page on Smithfield's website gives similar instructions to the one you're following:


  Preparation
  
  Genuine Smithfield and Country Hams (Cooked)
  
  If you have selected a fully cooked ham, further preparation is unnecessary. Simply slice
  and serve. If you prefer, reheat in aluminum foil on low heat (275 degrees) until
  slightly warm.


So if you want it significantly hotter than slightly warm you're going to have to do something different than what they suggest. You could try raising the temperature, the USDA recommends a temperature of not less than 325F in order obtain an internal temperature of 140F.