What are some of the nissan titan computer problems?

Of the number of complaints about the Nissan Titan, none seem to include anything about the computer -- assuming you're referring to the engine control module and related hardware. The only common complaint that could even cursorily be tied to the term "computer" is a persistent disc read error on a failed navigation unit, but not likely to be what you meant. The largest complaint, far and wide, is leaking rear axle seals, typically caused by lack of ventilation and overheating factors. There's also a fair number of reports of a clogged catalytic converter, caused by malfunction of the fuel pump. A catalytic converter replacement will cost you a pretty penny, as new units typically cost over a thousand dollars.