I would, and did, replace all four of mine with LR E. I had the rims to support the pressure increase as I suspect yours does too if it came with LR D tires from the factory. You could have the tire dealer check to see if the pressure or weight rating is stamped or printed on the inside of the rim, most are.
I would replace all four with radials as they are right at the end of their recommended lifespan. My old tires had quite a bit of tread left so I put them on Craigslist and sold them right away to a local guy who wanted them for a utility trailer. I explained in the ad that they were 6 years old but he didn't care. The price was right.:)
I replaced mine with Maxxis but I think if I were to do it today, I would go with the Goodyear Endurance which is getting good reviews both here and on other websites. If you have to get new wheels also, I would consider measuring and see if 16 inch wheels would fit. That would give you a lot more choices when buying tires in the load ranges you need.
Barney
2004 Sunnybrook Titan 30FKS TT
Hensley "Arrow" 1400# hitch (Sold)
Not towing now.
Former tow vehicles were 2016 Ram 2500 CTD, 2002 Ford F250, 7.3 PSD, 1997 Ram 2500 5.9 gas engine