[Screemincheetawheely]

I just installed a used 4l60e from a 99 tahoe into my 98 sierra.
I have 2 issues, first being that when driving in overdrive at higher speeds the truck will shudder for a few seconds, then stop for a bit, then shudder again and stop after a few seconds and will continue to do this until I shift to 3rd and leave it there. Also seems like the TC is locking and unlocking at a lower but steady speed.
Second issue is weird, while shifting from 3rd gear to OD, right in the middle of the 2 said gears, the starter engages.....What the......!
Any advice is a great help guys.

Thanks, Mike

[Hanr3]

Could be a couple of different things.
I doubt the starter is engageing, rather the flexplate is hitting the starter. Either the flexplate is loose, cracked, you didn't engage the torque converter completely into the tranny when you did the swap, or the trany to engine bolts are loose.

The shudder could also be the torque converter not completely in the tranny pump, loose tranny/engine bolts, or lack of lock up.

One last thing, got enough tranny fluid?