Bike wont accelerate much on 5th gear and starts to deaccelerate and loose power ( honda xr 125)

[LoganZAR]

Hi ,So its hard to write it down exactly as its a strange thing that i am trying to word but around 1k kms ago i got a new top end installed and all was fine.I just did a new oil change afew days ago and since the super windy days i cannot accelerate past 80-85km without my bike basically stopping power all together and sometimes i need to drop gears to gain power back.It doesnt happen in gears 1-4 but mainly gear 5.I tested today on the one day without wind and it did the same so im worried something is wrong.Could it be that i need to change my air filter? Hasnt been done in awhile.I know these bikes are basic so i dont know whats at fault here.

Any help would be MUCH appreciated.

 

[Jacobsroodt]

 

[TheBear]

 

[Tommy Transalp]

 

[petri oosthuizen]

 

[petri oosthuizen]

 

[BuRP]

 

[petri oosthuizen]

 

[Skaiidawg]

 

[TheBear]

 

[silvrav]

 

[LoganZAR]

 

[LoganZAR]

 

[LoganZAR]

 

[LoganZAR]

 

[sidetrack]

 

[TheBear]

 

[BuRP]

 

[TheBear]

 

[AfricaOffroad]