Highway shudder
 

When driving at light load on the freeway and just rolling into the throttle I get a shudder like I hit a rumble strip on the side of the road. Its hard vibration wise and fairly audible shudder. Only lasts a second or so, any ideas?

Could be a few things. Maybe be the rear end, maybe be the drive shaft slip yoke, or the transmission.

I have had that same issue. Turned out to be a misfire, and 8 new plugs cured it. When was the last time your plugs were changed?

^^
Yup, the rumble strip description is usually a misfire..
Coils and or plugs will fix it if you haven't already had a recent tune up..

I just replaced the plugs 1500 miles ago when I did the exhaust manifolds. A miss fire should throw a code or a check engine light should it not?

It will only throw a code if it happens several times.

You should have a look at the coils and boots and make sure the connectors are seated and the boots are properly greased.

It also probably couldn't hurt to check the Trans fluid too.

My truck does this as well. Cruising 60 on the highway lightly step on the gas till it shifts and when it down shifts from o/d to third it shudders, it will do this every time in this situation. If I really step on the gas and make it shift there is no shudder, been wanting to change all drive train fluids for a bit now just have not gotten around to it so not sure if it would cure it or not. Changing the tranny fluid would probably solve it for me 120,000 miles and I am pretty sure the fluid is original.

I just changed the fluid last June and did the spark plug boots and greased them when I did the plugs. It never downshifts while this is occurring and the fluid is not low.

Did you replace the boots and springs? Or just grease the boots?

Interesting)