transmission issue?
 

2008 with 137000 miles.The truck on occasion has a hard time shifting from 3rd to 4th gear. gas pedal to the floor rpms at 2100 and turbo gauge only at the 1/4 mark . it has a little surge feeling then it might shift. truck has the problem either in or out of tow haul . do not know if that matters. I have had the truck since it had 81000 miles and no issues until now. any thoughts on this ? thanks in advance

Sounds like the 3-5 shift flare issue. Does it do it worse when cold? Any issues when shifting into reverse? There's a modified direct clutch solenoid that addresses this issue but with that many miles on truck your direct clutches may be starting to wear and that's why you're noticing it now.

no issues with reverse . I pull a 6000 lb trailer and have seen it twice when pulling it. I pull this trailer 3 times a week. have not seen a problem when cold. it seems to more of a problem after I get to where I am going and truck is turned off for a couple of hours . then on the way home is when the problem starts.

Interesting....my truck would have the 3-5 shift flare every now and then. I changed the direct solenoid to the GOGO modified one. All 3-5 shifts are now crisp and firm. Apparently the stock direct solenoid doesn't flow enough fluid to engage the direct clutches fast enough so they slip (flare) a little bit. As they wear this little slip can become more noticeable. I'd notice it slightly more when cold as the fluid is thicker so it would be more pronounced then.

Some of the basics. Checked the fluid? Ever change the filter and do a trans flush or at least fluid replacement with a new filter?

If this is a 2008 if it is job one truck then you may also have the external filter as well.

the mechanic said the code showed extreme high fuel pressure he gave me a 50 50 chance that we could fix this by putting the factory program back on the truck if not then he recommended that we would have to replace the high-pressure ignition pump I have done the EGR and DPF delete on this truck this is my first diesel and this is way out of my knowledge league