... As i'm reasonably tall at 6ft8 ...l
Welcome to the forum; you might want to start over with a new username.
Might I suggest "Master of Understatement"?
First off, this is not a doohickey issue. Were it that, you'd merely hear noise indicating a need for adjustment.
What you describe could be related to the removal of the restriction, but it could also be lean surge. A 22cent mod could fix that. Lean surge is usually gentle, kind of an "unnnh-unnnh" feeling.
You describe it as being more of a violent, sharp sensation, so it also could be that the transmission is not fully engaged in top gear and is hunting a bit between 4th and 5th. The transmission is a constant-mesh unit, so this is possible.
Most KLR riders shift into 5th gear and then, out of habit or desire, reach for 6th. Try this reaching for 6th routine to make sure that the bike is firmly engaged in top gear just to eliminate that as a possibility. You may find that your feet don't fit the peg-shifter span well, causing upshift issues. You can cure that to some degree with an extended shifter, and you can rotate the shifter lever around on it's shaft to a more comfortable position.
Diagnosing over the internet can be tough, at best. Have you any other symptoms or conditions under which this occurs?
By the by, since you're at 1800K, you should adjust the doo. Using a 1/4" drive ratchet, crack it off, rap the back of the ratchet with the handle of a large screw driver several times, then re-tighten the adjuster bolt to no more than 9Nm.