I have a 1989 Fleetwood 37J with a Ford 460 engine. Problem I have is when under load I cannot get it past .15 MPH. At idle the engine runs great. I thought it might be the ignition module but thought I would try to get someexpert advice first. I have only had the RV for a few months and it did do this a little but now it is all the time. I tried letting the engine warm up first but it didn't help. Any advice provided would be greatly appreciated.