Truck shudders

[DaveNY]

I have had this problem for quite a while but seems to becomming a little hasher as of late.
Right at 45mph when the converter locks up and is given light throttle the truck shakes like a bad U-Joint untill 48 mph then completely disappears??????
Really feels as if it were the engine rather than the drive train which makes no sense at all.
Maybe something in the converter?
If I lift my foot off the throttle smooth as silk.
A little puzzled
Dave

[DennisG01]

What's the level and quality of your transmission fluid?

[DaveNY]

The color and level is ok and it smells ok.
Bought the truck w/69K on it and 199 now with no filter or change. Against my principals to let it go this long,but have heard more than once if the fluid looks and smells ok leave it alone?