While checking the other items suggested above, and before buying a whole bunch of parts, please check some of the small/simple (below) things which can also cause what you're describing:
Lower Radiator Hose: Plz check your truck's lower radiator hose. It's possible a new hose w/o a spring was installed, or the spring wasn't re-installed on the existing hose, or is installed not in the center where it needs to be.
That can cause a hidden condition when the coolant is warm and the hose becomes much more pliable, the sides of a hose can collapse into themselves under heavy suction and starve the water pump (of coolant) under acceleration. But let up off the gas and it goes back into shape ...(cruising or coasting) and sufficient coolant flows. I've seen it before. Simple to check; just grab and squeeze the lower radiator hose to ensure there's a spring or form inside. Squeeze along the hose to make sure there isn't a certain area where there isn't much spring. Sometimes springs can work themselves up close to the engine ...and there could be enough space near the radiator to 'suck-in'. Wouldn't hurt to have someone rev the engine and watch it too (when coolant is hot).
Drive Belt Routing: Double-check the drive belt routing is correct. I haven't heard this on Ram V6's ..but on some engines, in rare cases, it's possible to route a drive belt two ways and still tension. On such engines it's a simple mistake to route a belt incorrectly. And if that happened it could spin the water pump backwards. It probably isn't your truck's situation, but, there's always a chance ...it's something that should be verified. It's super-easy/quick to do, and doesn't cost anything to inspect (compare to a correct belt routing map of your engine/year).
Slipping Water Pump Impeller: Another issue I've seen that can cause your symptoms, which is tricky to spot, is, a slipping water pump inpeller. Sometimes an impeller can feel 'tight' when cold (when a person would normally check an impeller by hand), but when hot the impeller can loosen. But not enough to quite slip during normal crusing speed driving, EXCEPT under heavy stress (like spirited acceleration). If you rule everything else out that's been suggested, it's something to look at. If you replace it, don't go to a part's store ...get a Mopar W/P.
Mis-installed Head Gasket: or failing head gasket: This is one where it can be real tricky to uncover ...and the only way you'd know it is if none of the other 'fixes' did the trick and you removed the engine's heads. What you could do now is when the engine is warm squeeze the upper radiator hose and it should be stiff and under pressure, but not feel like it's got 2x, or 3x more pressure than normal, or appear 'ballooned' out. And with the radiator cap removed, run the engine and sniff for combusted gasses ...and observe for bubbles while someone rev the engine. Do you hear a 'water gurgling' sound in the heater core in the am? Looking at the spark plugs (for a REALLY clean one or two) would be another indicator.
It's not likely to be the problem, but parts can fail prematurely, a headgasket could get knocked on the floor and a dog could walk on it (bend the corner of the head gasket) ....people and engine builders are human and screw up. Stuff can happen. And if it gets installed upside down or backwards (if it's even possible on these engines), then coolant holes could be blocked or partially blocked off. I'm not sure if it's possible to install the HG's wrong on this engine, but many engines (most) ..it is. Most head gaskets are marked 'top front'. If a guy gets a phone call from a crying spouse/mate/kid, etc during that phase ...sure, a mistake can be made. I personally know a few people who've had this happen over the yrs. It really can't be 'tested' during QC, ...and it takes an expensive head-removal job to finally get to the bottom of it. And I've had or worked on people's cars where head gaskets failed (usually delaminated) prematurely. Again, not likely the culprit, but certainly possible. A failing HG would exhibit the issues I listed in the paragraph above ...those you can literally 'sniff-out' ...lol
Good luck,
Let us know what it turns out to be.
