We just purchased a 1990 Ford F150 XLT Lariat 4x4 w/ 162000 miles. Has a rebuilt motor w/ only 22000 miles on the motor. The fuel pump was replaced 1 year ago. In order for the truck to start after it has sat for a few hours, you have to turn the key on for 30-45 minutes. You can hear the fuel pump. And when the truck does start, you have to put it in drive 1 to take off, then put it up into drive or there is not enough power. Any suggestions as to what could be the problem?