In the early 1990's we had a real close call doing exactly what the OP has described.
We had been using a rigging block and bull rope attached to a 4ft. diameter bald cypress at about 50ft. height to pull over about 50 smaller trees that leaned towards a fairly busy road. If we felled them into the swamp we didn't have to do cleanup. I had rope climbed the cypress early that morning to place the rigging block. We were using an older Chevy truck for the applied pull and there were no truck or driver failures that led to our mishap. It all happened in about six or seven seconds. I'll never forget his screams of terror as he realized what was happening.
To remove the block it was decided that one of our climbers would 'ride the bull rope' to the attached block, tie in for rope climbing, and lower the block out of the tree. The 5/8 inch bull rope was about 250ft. long. What happened was that when the climber was at about thirty ft. in height his hanging lanyard loop caught on a small natural stub bringing his ascent to a temporary halt as the truck continued to move forward stretching the bull rope with applied stored energy. The lanyard came off of the natural stub and the climber was sent into a 'reverse bungee' and ending up crashing into some lower canopy limbs. He dropped below the canopy limbs and hung unconscious for about sixty seconds while he was being lowered back to the ground by the backing up truck. He came to a few feet off of the ground and other than being shook up a bit was fine. We feared he was dead.
To get the block down I got on the bull rope and few minutes later and you can bet I was careful of where my lanyard and other gear was hanging!
We all went home safe and sound that day but over 20 years later you can bet that I learned a very valuable lesson that will stay with me for life.
If you've got three or four strong men on the ground I highly suggest to use them to pull a climber back up a tree Vs. a pickup truck. That way if there is any 'snag' the 'system' will not be exposed to the tremendous forces that can be generated by engine powered equipment.
Trust me, it's not a good experience seeing one of your employees hanging unconscious on a rope. I get choked up just writing about it even now.