i installed a 350hp tbi in a 1990 suburban do i need to upgrade the computter or wiring harness  

Off topic, but how did you sqeeze 350 hp out of a tbi trcuk, 383 stroker kit? You should probably have a custom chip burned.  

this engine was custom built by a company in arizona. they did a really nice job but when i installed it it ran unreal for about 2 days then i started gettin the check engine lite and she started spittin and sputin, losing power and i had to hold the pedal down to clear it out then it would run good for a while and start givin me a hard time again. check engine lite is flashin on and off seems like electrical problem question is can a stock computer recognize and run this tbi replacement?  

you could always start by going to any parts store and buying an Actron code scanner.  The one for that truck is about $24.99. snap it into the diagnostic conv. and if your check engine lite is comming on it should tell you why. those worked great on my 89, and it is a fairly cheap and easy place to start. 

I would definatley recommend scanning it if the check engine light comes on, sounds like fueling issues though, look into a custom chip for your truck