99 Denali Overdrive Surge

[eg30.06]

I have a 99 gmc yukon 5.7l. Starts runs and seems to drive great until it goes in overdrive. Once I get TC lockup I get a 200 rpm surge as if it were to come out of lockup and then rite back in. I can't really feel it but can hear it with the increased engine speed. Does this whenever cruising in OD, every 5 seconds or less.
Thoughts?

 

[stutaeng]

Any additional information?

Was it working fine before? Have you done any kind of mods? Got any CEL on your dash or have you checked for stored codes?

 

[eg30.06]

Any additional information?

Was it working fine before? Have you done any kind of mods? Got any CEL on your dash or have you checked for stored codes?

Bought it not running due to fuel pump. 100 percent factory, no check engine light. PO said it has a jasper transmission in it and verified with receipt. Has 30k on the transmission.

 

[Knuckle Dragger]

Bought it not running due to fuel pump. 100 percent factory, no check engine light. PO said it has a jasper transmission in it and verified with receipt. Has 30k on the transmission.

There's your problem

 

[eg30.06]

Anyone?

 

[gearheadE30]

No check light doesn't mean no stored or pending codes...might be worth checking anyway. Misfire counts can cause the transmission to cycle in and out of lockup. They may have also put an earlier 4L60 in that isn't compatible with the EEEC converter control that truck uses, which does not completely lock the converter until you are over 75 mph or so. Any other issues with driveability? Has it always done this as long as you've had it, or is it a new problem?