When's the last time you had it tuned up? Have you tried running some Seafoam through it?

Water injection can net you some extra power a whole lot cheaper than a supercharger.

1998 T-100 Xtra cab SR5 2WD Auto; Roadmaster Active Suspension; Yokohama Geolander HT-S; lowered air dam; full belly pan; 4? diffuser; 11" side skirts; dual transmission coolers; 67% grill blocked; Auto-RX'd; ScanGauge II/Ultra-Gauge