I-40 is your most direct route, just be prepared for some hills and curves. once you get thru the gorge, there is 2 short tunnels too with plenty of room, the road gets somewhat flatter and straighter. Taking a 5er thru Pigeon forge is fine but Gatlinburg is another story. G'burg is tight for pulling a 5er thru but your truck will do fine. The closest parks to Dollywood are the KOA and Bear Cove Village. My suggestion is to get off at exit 432 headed west, 25w/70 (2nd off ramp heads west, first one is east) and connect to 411, its a short distance from the exit to 411. 411 will be a 2 lane and curvy road at first but semi trucks use it so you will be ok with your 5er, just take your time. you will go about 15 miles to Veterans Parkway and head south(left turn, only way to go). Both parks are on Veterans Parkway and you will miss the really heavy traffic on the main drag, 66/421. The trolley goes all the way to G'burg too but you may have to change trolleys once or twice.