You can (now?) upgrade as much as is available, i.e. as many rooms as you have cash for, if you have reached the level when teh upgrade becomes available.
I like this game, it is nicely done and gets me into teh flow; the only nit to pick is that I often "use" a person that has a tutorial note attached before I read it; in a game that is so swift there should be a way to re-read that.
Needs an option to switch controls, this is counterintuitive to me. I want the right arrow to control teh right nozzle and the left arrow the left, which makes me turn when I release a key.
The conecpt's nice, but the controls, the graphics and the non-flow feedback when I make mistakes put me off. A game that punishes every istake by having to restart the level is bound to be frustrating.
Look at the games that DifferenceGames uploaded, they are the best. Yours is ok, easy, too, but doesn't even come close in the way the interface works and the subtlety of the clues. (DifferenceGames always places at least one more difference than you need to find to pass, too.)
Once I realized how the trailer is connected to the tractor (not at all, basically), I could complete level 4 in the first try. (And I got about halfway through with the pickup truck before I bought the trailer. ;)
I did level 3 with the starter truck on the first try, delivering all 3 goods. Where's the problem? The game would certainly benefit if it felt more like Crazy Bikes, but the tasks are doable and the physics are challemging but not impossible. You just have to learn to not keep your foot glued to the accelerator.
To translate this type of puzzle to interactive media, a lot more needs to be done (why intermediate points on a straight stretch of K? learn about splines, too!), and there is no motivation in it either. It needs Zing!
 "Adventurous Eric")
 "Hotel Management")
 "Jetpack Jailbreak")
 "Stay on the raft")
 "Maverie - The Mad Scientist")
 "Miki - The Space Police")
 "-The Siege Of Theldale-")
 "Matter Shift"){kind=icon}
 "Cool Anime")
 "Truckster 2")
 "Dot To Dot: The Dottening")
 "Hotspot")
 "Frontier")
 "Halloween Kiss")
 "Halloween Icecream")