The two main companies that most guys on this site go to for the auto tranny is either SunCoast or HTS. A lot of guys have had good luck with HTS parts and they are family ran and friendly. Best to call Dusty or his wife and explain you have the SRT-10 with auto tranny, they will get you hooked up based on your NEEDS, they won't try and oversell you on uncessary parts.
For exhaust, there's a lot of opinions. Out of the box the Billy Boat exhaust probably sounds the best and offers the most gains in hp/tq, but it's EXPENSIVE. Best bang for your buck is to get your rear cats removed or just get catless midpipes, get the rear resonator by the exhaust tips removed, then have welded in some mufflers of your choice. Which mufflers to use will vary from member to member. Some guys like the exotic sound or exhausts have, some want more of a V-8 rumble. I currently have rear cats deleted, Flowmaster-style off-brand mufflers, rear resonator removed. It soulds pretty good for a 200 buck exhaust lol.
Most guys prefer the Mopar factory waffle comb grille that came standard on the 2500 series Diesel rams. They are cheap, easy to install, and look great. That's what I have.
For lights, you can find any kind of headlights on Ebay. Or you can look in the vendor section on here for the vendor Retro Shop. My headlights are factory ones that someone blacked out, got them from a member on here who got them from Ebay. I love them. I also have HID headlight bulbs and fog bulbs.
For some other visual upgrades, check out jmbperformance.com. Justin has some great engine bay visual upgrades, does caliper powdercoating, and offers custom Viper emblems.
For performance, in terms of all-inclusive websites, roeracing.com has most everything you would ever need to do a complete engine rebuild, cam swap, exhaust, etc. JMB has some options as well on his site, but better to contact him directly, he can get you most anything. Also, another great vendor is Venomous1 (Scott). He can direct you based on what you're wanting to do and he has some of his own parts available.
Hope all of this helps.