u r right DX comes with radio,but many importers add navigation and even power windows,power side mirrors at the port to increase the value of the vehicle,they take out these things from damaged vehicles at khi port,i ve seen this myself.Have u changed engine oil.transmission oil,air,fuel and oil filters.then drive for sometime if u feel like then get its throttle body serviced and engine tuned.Get these from toyota 3S workshop,while getting transmission oil changed keep an eye that they use TIV transmission oil.regarding oil i am using liqui moly 5W-40 fully synthetic and i am satisfied with it.read the forum u ll find many good suggestions/experiences which our dear brothers have shared,it may help u alot