Wolf Hobbies posted about not soaking the belts. They posted to soak the bearings in denatured alcohol for a few hours and then spray them off. Relube with lite bearing oil and that will really help with freeing up the car. I don't think his post is more than a few pages back on this thread.

Here is their post from Wolf Hobbies. Its on page 148 of this thread.

As most of you know we had a great result at the Reedy Race. We have to say that we are overjoyed with Dave's driving and how far we have been able to develop the car in the last year. Also as you may know we get zero assistance in our race program from TM so it has been difficult to share all the info with all the racers. We will be posting on RC Tech and other forums to get everyone up to speed (pun intended).

E4 speed secrets part 1:

There has been a lot of discussion about freeing up the drive train. Most people point a finger at the belts. We have tested every belt we can find and are working with a manufacturer to make some special belts. Until then we can say that the stock belts work very well if they are adjusted properly. We can also say that the belts are not the problem. The problem is with the bearings more specifically the grease used by the factory and the quantity. We have developed a treatment for the bearings that really makes a difference:

We recommend that you soak the bearings in denatured alcohol for 4 to 6 hours. Denatured alcohol is highly flammable!!! Use with appropriate caution.
Do not substitute any other type of alcohol, as other types of alcohol are not an effective solvent for the grease that Team Magic uses in the bearings. Additionally, most types of alcohol will absorb moisture from the air, and will cause the bearings to rust. After soaking gently blow out the bearings with low pressure clean dry air to remove the alcohol and dissolved grease. Repeating this process is a normal part of maintaining the car between races. No oil is required the first time the bearings are cleaned, but it will be necessary to re-oil the bearings on subsequent cleanings. This single step is creates an amazing performance increase. Once the car is back together it is critical to adjust the belts properly. The easiest way is to set the trim on your transmitter so that the car is running at about 20% throttle. Tighten the tensioner until you hear the motor slow down. At that point you know that the belts are too tight and back off until you hear everything running free. We did this test with a tachometer reading the spur gear rpm and saw how dramatic the speed of the car drops when the belts are too tight. Just so that it is clear. The problem is not with belt drag. It is friction on the bearings. If you still have a problem with the side belt slipping it can be cured with our P/N WH10117. This fixes a design flaw in the kit and not only fixes belt slipping but makes the car solid under hard braking. One final word on WD-40. Don't use it on the belts or bearings. It seems like thin oil but it has two components. One is a light and very volatile oil solvent and once that evaporates it leave a gooey film on the bearings that creates a lot of drag. Using it on the belts might give you the feeling that you are making them more compliant but you are also making the teeth on the belt soft which leads to slipping which makes you tighten the tensioner which makes the car slower than leaving the belt dry.