Past 2 days I get this problem with my car, when it shift on 2nd gear it feels like it doesn't have that much power and it gets higher rpms.

hey man i got an 00se auto and i had the same exact problem it turned out to be that my 2nd gear band was shot in the tranny. i really hope this isnt your case but thats what my car was doing. good luck bro

What do you mean by "it gets higher rpms"?

Also edited your thread title to something that is actually informative.

when it gets on 2nd gear and if you want to accelerate little bit faster you have to push gas pedal much harder than it was before, and engine sounds on 2nd gear kind of like its an 4 cylinder car, or few cylinder not working.
(It's hard to explain).

check engine light on?
mileage on vehicle?
most likely coils or maf

check engine light is off, 80,xxx miles.

I'll second the bad coils or MAF...

In order to help use diagnose your problem, let's try this: Does the car pull hard up to a certain RPM (regardless of gear), then the pull drops off at and past this RPM? For instance, my MAF died after I disconnected the negative terminal of the battery. I noticed it when my car would pull hard to about 3.5K RPMs, then the pull would drop off, but the RPMs would continue to climb.

hey did u check ur tranny fluid? cause i remember it kinda smelled weird after u punch it....might be the tranny slipping

well I checked tranny fluid and its okay, it seems that I get this problem when car is kind of cold.

Does the slippage go away once the car is fully warmed up? If so, that seems to be a problem with 5.5 gens. Something in the valve body hangs up when the transmission is cold and causes soft or slipping 2-3 upshifts. A couple people have installed the Trango Shift Kit and solved the problem, others have had the valve body replaced under warranty.

my 2nd is different than when I bought the car.
when it goes to second, it feels like it slips a bit then graps.

i think we should start posting vids of these late shifts and compare....everyone seems to be experiencing something a little different...or explaining it a different way...

I tired, it's really hard to tell in the videos, it's more like a feel thing.