engine cut out- leaning out?

[93SilverBullet]

Have a 93 gt, complete overhaul done-302 bored .040 over(308), tfs stud girdle, ford y303 heads, f cam, 1.7 ford roller rockers, trick flow r series intake(upper and lower), 75mm tbody and egr, cold air intake with matched maf meter for 24 LB injectors, hooker headers, dynomax bullets w/no cats, h-pipe, 410's in rear new t-5 tranny along with cobra clutch....heres the PROBLEM- i notice this especially in 5th gear, once the rpms hit about 3000 or speedo is nearing 100mph, motor starts to cut out and backfire, but in all other gears its fine and in 4th i can take it to 135, but soon as i shift to 5th it starts bogging down...fuel starved? if not any suggestions on what it is and how i might can correct it? thanks