stock 95 mustang gt 5.0 help

Do you mean it idles high for 3-5 seconds? I can't see any link between filling the tank and an idle condition but was wondering how low you let the tank get to before filling. The pump immersed in fuel keeps it cooler and was wondering if there might be a link between an old overheated pump and fuel delivery. IDK, just a thought.

please learn english so we can understand you

I understood him just fine. He's saying when he fills up the car seems to have much more power for a few seconds then goes back to normal.

I'm with Richard, I think the fuel pump is in it's final days and when it is submerged and started, it remains cool and puts out max pressure for a few seconds before heating up again.

Also, the vent hose leading to the charcoal canister might be clogged/kinked and thus causing pressure issues in the tank. Taking the cap off could relieve excess pressure and allow the car to run normal for a few seconds until it re-pressurizes. Just brainstorming, there's no telling without seeing it first hand.