need help please

well i finally got around to pulling the gas tank and i found my problem, i cleaned the gas tank and the filter
on the sending unit well when i went to put the gas tank back in i wanted to double check where my evap hose went. I work for a garage and we have alldata, it showed me where the hose went and i had them crossed from a previous time when i had the tank out to replace the sending unit. I filled it up with gas this morning and everything is working great. thanks for the help guys. I do have one other problem its not really a big deal but it would be nice to fix, My truck won't go over 4,000 rpms not that it really needs to unless going up a
really steep hill but i would like to fix it, and the mechanics here cant find the problem so any input on this would be appreciated. thanks

what exactly does it do at 4000rpm? if you can explain how it acts i might be able to help

The best way i could descibe it is it feels like its hitting rev limiter.

ive, kinda been ignoring this problem but just keeps bugging me i thought maybe my 2nd barrel wouldn't open
but its working fine, i adjusted the timing its fine but it won't go over 4000 rpms and when i hit that it stumbles and feels like hitting rev limiter like its governed their or something but any help would be
appreciated. thanks in advance

Check the vacuum advance.

When they go bad, you will get the sympoms you are describing.

Here's a thread which deals with a bad advance unit:

thanks for the help guys i think im on the right path now