5 on a trailer would be 3,500 plus another 1000 or 2000 for the U-haul trailer. Clearly too much. 3 in the bed would be 2,100 lb with much of the weight towards the rear of the bed. Too much.
Check your GVW - empty weight load rating, like others have advised and see if it's close to 1,400 lb. You can probably handle 1,400 lb. Put the mill drills as far forward as you can and raise your tire pressures to the max listed on the sidewalls. Shouldn't be a problem for short trips as long as you don't bottom out the rear suspension and I doubt that you will.
5 is a good number, move one the first trip and see how it goes. If it feels like you have a lot of reserve capacity, move two the following trips.Do you have a good way to get them out when you get to your destination? I unloaded my Mill/Drill using a ramp and almost dropped it. Gravity is a bitch.
Dick