I hit 388HP on stock non-intercooled sticks. I would take the money that you were going to spend on injector's and buy gauges, a 4" exhaust, a high flow air filter (not a k&n), and build a high flow intake tube.
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04.0 HO QC 4x4 LB auto transgo VB, stock, for now
Sold 91 now intercooled W250, 388HP 923TQ on #2 only 436HP 968TQ on meth
Work Truck, 93 W350 LE Dually 5Spd almost stock