What you are describing is called porpoising. That can be alleviated by a better hitch adjustment. You need to get weighed period. Go to a local cat scale
to get weighed. You have several nearby. here are your nearest 3 locations.
It is usually $9-12 for first pass and $1-3 for each reweigh at the same scale in a 24 hour period. You will want to bring a long stick or broom handle to reach the truck height button. When asked for a truck number tell them private vehicle. Some will want you to make up a number... pick your favorite number it doesn't matter.
The truck should have all occupants, gear, and pets in it that will be in it when towing plus full tank of fuel. The tt should be loaded (mine has the usual stuff minus food when weighing). When weighing you will want to do a minimum of 3 passes. These can be done in any order.
1st pass is truck only. Front axle on scale pad 1, rear axle on scale pad 2.
2nd pass is truck plus tt no wdh. Truck same as pass 1, all tt axles on scale pad 3.
3rd pass is truck plus tt with wdh. Truck and tt same as pass 2.
Use the first and 2nd passes to determine total TT loaded weight and tt tongue weight. Ideal tongue weight is 12-15% of loaded tt weight.
Use the 1st and 3rd passes to determine efficacy of your wdh. Goal is to get the front axle as close to unloaded weight as possible without going heavier. We used to bring tools, hitch in the parking lot, make an adjustment, reweigh and repeat until correct. When getting the truck only weight, we park the tt in a near by truck parking spot so we don't hold the scsles up. Same thing for wdh connecting/disconnecting/wdh adjustment.
It is best to do this yourself. Most dealerships do not set wdh up correctly.
The other thing to look at is tires. What are you running? Do you have LT or P rated tires? What are they rated to carry? What are they inflated to? What tupe of tread (ie mud tires typically have more bounce when towing).