Jerking top kick diesel

GMC guy

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#1
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Gmc
5500 duramax topkick
2005
374k
6.6 alison auto

Truck operates well from 1st to 2nd but from 2nd to 3rd it starts revving like tapping on the pedal and it wont switch gears and change to drive unless i ease back on the pedal. On highway, it is good in drive but when trying to get it to kick in to overdrive, it does that again until i let up on the pedal. Or if im trying to get it into overdrive and push the pedal it just chokes out and the truck will begin slowing quickly. I let up on the pedal and it changes to overdrive. Once im going up a hill, the truck will try to gear down and just chokes out again. I will check the fuel and air filters but im also thinking vacuum. Thanks
 

kev2

wrench
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#2
did you scan ?