JLG Lull 944E-42 will not accelerate or move in cold weather

Hello, the company I work for bought a 2005 or 06 944e Lull this past summer. It worked great all summer. A few days in late fall it got down to around 35 degrees it started acting up a bit. Driving it seemed to have a loss of power and surge. After driving it awhile the problem would go away. Now that it is full out Winter it seems to get worse the colder it is outside. For example today it was -4 degrees outside. I had it plugged in all night and it started just fine. I let it idle for 30 minutes. Went to drive it and it would not move one bit. I hit the accelerator pedal and it acts like I am doing nothing. Te engine would not even rev. So another 15 minutes later I decide to shift it into reverse and then forward over and over. I would get it to slowly move a couple inches then a couple feet then finally I got to a point where it would drive but barely. Driving it in reverse also helped way more than trying to go forward. Still I would have the pedal to the floor and it would act as if I was doing nothing, About every 15 seconds it would surge the rpm's slightly but that's it. It took me 15 minutes to go 100 feet into our heated shop. I got it into the shop and no kidding 20 minutes later I fired it up and it revs and accelerates just fine. However if I try to work with it outside it will go back to surging when it is cold. It is like there is no pressure in the fuel or a throttle position sensor is out but when it is warm out it works great. What am I missing? We use winter diesel fuel and I have changed all the filters. It is the Cummins engine in it. Thanks

JLG Lull 944E-42 will not accelerate or move in cold weather