How do I drive this forsaken dump truck (Backlash)?
The Dump Truck is by far the most difficult vehicle to use effectively in the game; but I've found a few techniques that have helped me get past the harder levels:
Practice using the Dump Truck on different terrain. One good place for this is the tutorial level. Particularly keep in mind that it handles differently on the (dirt? sand? whatever that pale ground is?) versus the asphalt. On the sand, it's much easier to start a powerslide but it's harder to angle it and regain control to get back to where you want on the field. On the asphalt you'll almost never powerslide without applying the breaks or unless you were already sliding when you hit it.
If you're not crunched for time on the level yet, concentrate on getting good slides and hitting at least something. This can make less work for you later if you hit at least some of your targets and can give you a little extra manuvering room.
If you're stuck on a level try different camera and attack angles. This is almost a matter of preference, but you might find it easier to estimate the timing of your slides by experimenting with the camera controls or how you approach the target.
If you're desperate, the Dump Truck can do some damage to buildings by ramming them head on. It only does significant damage if you have some speed, but even then this tactic is very slow. It can be effective if say you've partially damaged an obstacle and only need a few more hits before you've either cleared the path or will at least gain a significant amount of time.
If you're really frustrated with a level, try taking a break from actually trying to 'beat' the level and just slide into things, explore etc. For maps with multiple vehicles it might be possible to switch to something easier to use. But I've also found occassionally when I "gave up" like this, I managed to clear further than I had before (dumb luck, I dunno?) and actually did beat the level.
The sliding can only be done above a certain speed. I've found that grass slows you too much to be able to slide. I think RB is the button to push to begin power-sliding, but I'm not entirely sure as you can slide with the button, as long as you're going fast enough.
One thing that significantly helps is getting the Backlash in the air. Sometimes there's a ditch or rock near a building, run over that right before hitting the building. If you can get that thing in the air, it demolishes buildings easily.
If you're really fed-up with it, there's usually other vehicles you can find on the map. It probably takes too long if you're trying to clear the path, but finding other vehicles can make 100% completing the level much easier.