You can get real technical with the numbers.......but the fact is that is a pretty small trailer. If the truck is rated for 4,200 lbs. then why would it be unsafe to tow 3,800 lbs.? The manufacturer is not taking the liability associated with saying the towing capacity of the truck is in the unsafe range. It's generally the opposite, where the factory towing rated is very conservative.
The payload of a V-6 powered Ram is higher than the V-8's, so tongue weight should not be an issue. If you compare the rating of the V-6 3.21 geared version versus the 3.55 and/or V-8 it tells me it's only engine power causing the lower rating. The chassis (handling and brakes) are identical to the higher rated models. I don't consider engine power the cause for safety concerns when towing! it's whether you can stop and keep going straight down the road.