I have used a model 17 before numerous times. I can say this about it... If you don't have a loader of some form, get a model 13. The model 17 will chip I believe a foot of hard wood, and 15 inches of soft wood, or something like that. The only way to really stall that thing out is to force feed it with a loader (I have seen this many times). The 17 is good if you are clearing roads, or doing lots of removals in a big area. If you are going to be working in small areas (small driveways / neighborhoods) you will want a model 13. Also, for towing... an F350 w/ the turbo diesel is the LEAST you are going to want for a truck. The F550 with the diesel has no problem, nor would anything bigger than that. Don't forget that this machine weighs in at almost 4 tons. The times I have used the machine, for the most part was in land clearing jobs and it was being towed around by a track machine or something similar. If you think I am trying to bash the machine here, I really am not because I love it. I am just tryin to let you know of the "requirements" for one of those things. If all you do is pruning, this is not the machine for you. Keep in mind brand new they cost around $44K