When i was replacing my t-stat, i found that my old one was in pieces? my car ran hot only on certain occasions, i fixed that with a new radiator, 160 stat, and electric fan, (dang police cars were supposed to have improved cooling..yea right) Start with something simple as the t-stat, look into getting an aluminum radiator, check your oil for water and make sure you didnt lose a gasket.
Also the cobra computer sux, when you stomp on the gas does it happen to take 7 seconds to really pick up? Definately do the grs like you posted, you will enjoy the car more, with 373 you will enjoy it more, and gas mileage wont suffer real bad, but it will some.
Also if you really want to pick up some power swap the computer for an older a9l, the fuel and timing curves are way more aggressive, but if you just drive it normal, the cobra ecu wont hurt.
__________________
Police package 5spd 90 Lx, Stock original motor, 3.27grs, BM fan, fms 10.5 clutch, D&D quadrant, and adjuster, ADS chip, 180 stat, mac cai, mac h-pipe, mac subframe connectors, ASP crank pulley, ripper shifter, 26x10.5 M/T sport pros welds. 246 hp according to analyzer 
Race weight: 3,120
E.t-13.57 with 26x10.50's e.t. streets. 1.88 60'
mph- 99.92 mph
|