Literally the first time I heard this one, as in ticks only when towing. Many items are strained when towing, lifters tend to not be one of them. I can only guess if it is indeed lifters, you would be looking at a low lubrication situation, as in fluid either isn't there or there in less amount then normal and it is being squeezed out. Even if it was rollers it still doesn't hold up to theory of load and towing. It would be hard to figure how it would only do this under towing. My guess is maybe a lubrication strategy would help, again if it IS lifters. High molybdenum and ester base oils have proven themselves in low lubrication rams. That would be an easy route, a high volume oil might be another route. I would get a used oil analysis to see if there any wear showing up. At 250k miles you would expect no to low wear at best, so easy to see if there is an issue with that mileage.
have you checked oil level?
