Take the vehicle back to the tire store and make sure the tires were balanced correctly. Sometimes the wheel weights they applied when balanced fly off thus making the tire unbalanced. I just had 4 tires mounted and balanced and I made the dealer rebalance all four until they found the one causing the vibration. they found one wheel weight missing. Also...Dodge Caravans are notorious for transmission problems. A shuddering between 40 - 80 mph could mean your torque converter is going bad. Do not ignore this problem since the shuddering could eventually loosen the seal between your transmission and engine causing the fluid loss and burning. Also...check the rating of your transmission shop before you take it in. I took mine to Aamco and spent most of my time trying to get them to repair it correctly over a 2 year period.
Shaking at speed - probably due to poor wheel alignment or wheels needing balancing
get wheel balancing and wheel alignment done. you might have bumped it very hard .
It is scared of something, is there an Escalade around? Seriously, shaking while driving could be wheel balancing or front end alignment. Shaking while at idle or what seems to be coming from the engine might be a motor mount.
Are you sure the rotors are responsible? Check for tires out of round, or poor wheel balancing. Also check thrust angle on wheel alignment. Any of these can also cause shaking.
because wheels need balancing
It's probably shaking a lot because it needs its balancing done. Most tire stores like "Tire Works" will do your balancing for around $30.
As far as I have been told if it is shaking it needs balancing in the tires, if the wheels when you drive are shifting for one particular direction (left or right without being intended) then it needs wheel alignment.
Perhaps tires need balancing
How are your: Tire balancing, alignment, steering stabilizer? And did the shaking occur right after the modifying of the suspension?
Low pressure in the tires can cause shaking, the alignment can cause shaking also.
try adding transmission fluid and trans treatment if possible. If it is shaking while you are moving then your rims can be bend or your alignment is off.
The only that I know of is that you need an alignment.