stumbles

So I have an '85 Mustang GT with a 302 automatic and 3:73 gears. I replaced the engine with a roller motor I purchased from Blueprint Engines. The dyno sheet that came with the engine showed 9:1 compression, 308 hp and 344 ft/lb torque (at the crank). I put a Holley 4160 600cfm with vacuum...

150K miles, dual exhaust, cold air intake. Coolant flushed last year but looks muddy already since before I got it it went 5 years on a change. Ok so. This only happens when it’s hot out like it’s starting to get. Whenever I’m at idle (~750 rpm) and the fan kicks on it drops to about 500 and...