Fuel filler neck.After consulting with Filler Neck Supply in Washington state.
You DO NOT have to remove bed to replace fuel filler neck,looking under rear fender,IT'S RIGHT THERE.Easy replacement.Couple hose clamps,3 screws out side,and done.This is on my 06.Plus Filler Neck Supply is 1/2 cheaper for the neck
that i've found in town.

But if your hose to gas tank is shot,you may have to remove bed!!
see ya,old retired guy

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06 ranger XL reg cab
3.0 auto/3.73
stock except/30x9.5x15s
15x8 silver cragar soft 8s
white A.R.E. topper
93,500+miles

No you do not have to remove the bed to do just the filler neck, but if you have to replace the filler neck chances are the hoses are probably very brittle & should be replaced also as preventative maintenance, then you need to remove the bed.

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2000 Ranger Extd Cab XLT, 4X4 Off Road, 4.0L, Auto, 8.8 - 4.10's, 01 grille & lights swap.
69 Mustang, modified 5.0, & 5spd.(project)
99 Explorer Sport, 4.0 SOHC, Auto, 8.8 - 4.10's, PW, PL, PM, Cruise, Tilt. (Wife's DD)
05 F-150 2WD Regular Cab. ( My DD)