mbmtb, That brought back some memories.
Early in our figuring out how to hunt elk, I shot my first bull. It was actually in a spot where we could get our full size Bronco to it. I had dropped it on the spot with my .270, and it was actually in a decent spot to field dress and - we thought - to load whole. Ha! Fat chance. We opened the back of the Bronco and I pulled antlers from inside while my spouse pushed from the back. We both pulled, both pushed, and every time we almost had him in there a leg would leak out, then the whole elk was on the ground again. Keeping the head and antlers on was not helping. Finally I cut the beast in half at the top of the pelvis and sweating profusely and covered with blood we finally got him stuffed inside the back and slammed the tailgate. Whew. At least we weren't in the mud you were describing! It would have been so much easier to quarter him and load the pieces. Live and learn.
Years later we proved we were not much brighter. We got tags for elk on a private ranch in WY. Friend of a friend sort of deal, so we were at the ranch and I shot a nice large-bodied bull at the bottom a hill. The ranch owner was sure he could get his pickup up the hill from the opposite side, so the three of us set to pushing and pulling the whole bull up this hill. There was snow cover, and we only had a couple hundred yards to persuade this floppy carcass up the hill. This shenanigan started because some other hunters on the ranch were from out east, and had never seen an elk before. So somehow getting the elk back to the ranch house whole seemed like a good idea.
Cripes, what a dumb idea. Our host helped with the push/pull for a while and as we neared the top of the hill he left us to go get his truck. Alas, there was too much snow to get the truck up, and he left us to our own devices. So the two of us strained, grunted, and inched the bull to the very top. Then we had to get it to the bottom where a truck could reach it. Downhill, once started, worked much better. I sat on the bull and steered by digging his antlers into the ground like a mountain climber uses an ice axe while glissading.
There followed Act II of trying to load a whole elk into a container that was too small. Although I backed my truck into the slope of the hill, try as we might the two of us could not make the elk go into my little Toyota Tacoma, which had a cap on the back. Finally we gave up and went back to the ranch house to get the owner's full size, old beat up Ford with an open bed. The eastern hunters were all so excited about the elk, they piled into the pickup, and with all the extra help the bull was loaded amazingly quickly!
Ever other elk has come out boned, and in backpacks.