Check your tyre pressures.
Most vans come out of the dealers with the max pressure (stamped on the sidewall) in them. Put the MAM (gross weight) of your van and the tyre size on here and somebody will probably know what they should be.
I had the same problem with my first van. I put it on a weighbridge and then rang Michelin with the details. They gave me the correct pressures and it made a world of difference. I had 80 psi in and reduced it to 55 psi on their advice.
A bit off topic but I had my Tag axle van on a weighbridge this afternoon.
With a fuel tank 7/8th full and a fresh water tank showing half full, I was only 40 kg short of the maximum permissable front axle loading. I have removed the super king size mattress from the overcab otherwise it would have been worse.
The moral is: If you have a tag axle van, you are overloaded. :mad1: