LDV Maxus wont accelerate properly

LDV Maxus

my van starts and drives but going through the gears when you reach exactly 40mph it wont accelerate properly but if yu floor it in third and it reaches 52 it takes off like a rocket and no more problem till you drop below 52 and then its sluggish again

Wont accelerate properly

Hard to say what the issue is. If the check engine light is on you can scan the codes. The codes will help guide us toward the cause of the problem. You may want to try filling the tank at a different fuel station next trip. Could be contaminated fuel. Another possibility would be a misfire. If it has been a while since it was tuned up, you may want to start there.