SIenna shaking, what could it be?

About a month ago I backed up into a phone poll. Brakes were bad, and I didn't stop soon enough. Got the brakes fixed. I have a dent in the rear bumper and tail light. After the brakes were fixed, it started shaking, I thought only at high speeds, but can feel it even at lower speeds now. I have had the struts and shocks replaced. All new brake parts. Tires balanced and aligned. Found out two tire rims were bent so got two new rims and new tires. Still shaking. I can feel it at lower speeds, and it is really bad at high speeds. The garage is totally confused. They have no idea what it could be. I have spent $2000 on this so far! And not even had my dent fixed yet. My van is a 2002, with only 65,000 miles on it. Any idea what it could be? Could it be something from hitting the phone poll? I was literally just backing out of a drive way so maybe going 1 or 2 miles an hour. The dent isn't that big. And it only started after having the brakes fixed. But I took it in 2 days after hitting the pole. So can't say what did it. Any ideas? At least something I could ask them to check? I am dropping the van off tomorrow for a whole day so they can look it all over. He said the front end looks fine, tie rods and all of that. But since I did hit something, I am wondering if it could be coming from the back now? I have heard driveshaft, drivetrain, Ujoint etc. are any of those in the back? They say they checked over the whole front end. The two tires that remain are only 4 months old anyway. Great treads etc. There is no buldge in any tire. The rims are all new and perfect as of today. I need some idea of where to go next. Thanks if anyone has any ideas.

my :2cents:
I guess something could still be bent like the rear axle maybe. You have to check out EVERYTHING to make sure its still perfect if you hit anything at ANY speed.

my :2cents:
I guess something could still be bent like the rear axle maybe. You have to check out EVERYTHING to make sure its still perfect if you hit anything at ANY speed.

Good point. I will mention that tomorrow when I bring it in yet again.