Go with a reputable company, start with the airport/hotels. They should have several off-road options which may include 4Runners.

Malaria and Dengue fever are still risks. Get pills in country if you like or before if your health care provider can help. Best thing is to check out the W.H.O. site and the online presence of your embassy as they'll have more up-to-date info. Good rule of thumb though is that if you're not going to be going that far off the beaten path then you should be alright.