some thoughts I posted on a diesel board concerning lift choices...Pat has a 4 post lift that has wheels on it. So even with a truck on it he can move it around. Hopefully he'll jump in here with info.
It was good in theory, and like many of my theories, didn't work in practice.
It is a Bendpak 4-post 9000lb with dolly wheels. With 6400lb on it, it will not roll on the wheels, and struggles to lift 7000lb.
Since a lot of what I do requires lifting the tires off the ground, it is a poor choice. They do make $$$ trolley jacks ($1200 ea?) to lift the frame, but they are too tall in the down position for working on lowered vehicles (5" required) and too expensive.
When you want to remove an engine, the cherry picker won't roll into the front without lifting the truck 6" which makes it harder to work on.
My suggestion to anyone serious about working on Duramaxes and smaller vehicles is a high-quality two post with at least 10,000lb AMERICAN rating. My old two post was 11,000lb Chinese rating, which was truly dangerous with 7,000lb on it.
Mike L installed some very good units that I had the pleasure to work with. Very sturdy, contact Mike L for the model #.
Now some other thoughts:
The 4 post BP roller will actually allow you to move the lift if your needs require it. This is a big plus. We rolled the lift outside to pressure the underside of the truck. For a light car, you could roll it. It makes an excellent "storage lift" for putting 2 or 3 cars in the same bay. It is the best for fluid changes, shocks, exhaust, alignment, etc. It's only when you need to use a cherry picker or pull the tires that it's a PITA. It can be worked around easy enough, but you can get more work done per hours with the two post.
The biggest problems with the two posts are stability, preloading the suspension, and getting in and out of the truck. We have waxed frames that far inboard, so on a two post it can "creep" as you lift and lower, or do heavy work. I actually dropped Casper once due to creep, which is why I sold the 2 post. Weak models allow the truck to wobble, which can creep or cause other problems.
Preloading, is when you need the truck tires on the ground to do certain tasks like check suspension/alignment stuff. 2 posts suck at this.
Getting in and out of the truck with a two post sucks since the beams block the doors. So always buy the widest model you can find. Some of the narrow models will require you to push the vehicle into the bay or climb through the window. With a four post, you can even get in and start the truck when in the air.
There needs to be a new lift design, that shares the best of both worlds. Six post anyone?