What kind of mortgage do you carry on the property?
You could always see if you could convert it to a HELOC, minimum payments on a HELOC are significantly less then that of a mortgage. Maybe you would be able to carry both, HELOC on existing property, and your mortgage on the new property. Your financing would have to be re-done. But this is one of the instances where it has worked. I'm surprised you were able to secure financing for the new property without having your house conditionally sold.
Other option, if you have your financing in place, MTG on current property, MTG approved on new property with no condition of getting rid of previous mortgage, take out a small LOC.
Use the LOC to make your mortgage payments for the 2-3 months you are selling. You will have to pay interest on the LOC, but agian it is better then eating a large discount off the price of your current house.
These opinions are entirely my own and do not represent any other person or organization.