FL studios tempo issues

[splendidTRUSTe]

Hello, I have been working on a track in fl studio recently and i changed the tempo of this melodic dubstep song in the second build and drop so it could have more variation, I made each sample time stretched to about 4 bars or the time they were originally so they wouldent move and get off beat when the tempo was changing, Once i did this i noticed that all the samples were pitched up really high before the time change so i figured out if i press the mode and made them e2 transient or auto or resample again they would change back to the normal pitch, i then noticed that the pitch of all the samples started to fall and when the second drop hit all of the samples were really low pitch and sounded bad. Here is the track https://soundcloud.com/setrik/setrik-edge/s-yt2gc the pitch change starts at about 2:57 i want to know how to change the tempo of the track without affecting the pitch of the samples. please help