what year chevy? My 08 Silverado HD is rated for up to 1500 lb tongue with weight distribution...if there is a factory installed receiver there should be a label on the receiver with weight maximums. Sounds to me its your bars. I had that happen to me on my last trailer. The bars I had at the time were rated very close to the tongue weight. When I went to the 1200 lb bars the problem ended.
2011 Jayco Eagle Super Lite 314BDS
2013 Chevy Silverado 2500HD CC 4X4, 6.0 Vortec, 4.10 axle
Reese Dual Cam Sway
Wife, 2 kids and dog