Probably the first three things I would look at would be improper loading of the tow vehicle AND the trailer. Most weight in the trailer should be over the two axles if possible. Keep most of the weight in your pickup in front of the rear axle , again if possible. Also, item number two, would be checking to make sure your tire pressures were all on the money. Item number three is probably the most serious and that is the tongue weight of the trailer needs to be in line. A good starting place is 10% of the weight of the trailer, but that is not written in stone. You didn't tell us if you had a DWH by the way. And click on the link above to go over a really good check list on that sight.