Mention rhythm to guitarists and it's often associated as being the role of a rhythm player. Wrong. Rhythm affects us all, whatever role we play, and to maintain and improve it few approaches equal playing along to the humble metronome.
There are numerous ways to interact with a metronone. Many shredders go for the 'one lick/increase the tempo' approach. As the click speed increases, you keep up with your repeating three, four or six notes per click (npc) lick sequence. What are the shred tempos? Youtube shredders may demonstrate otherwise, but you're doing pretty good if your picking or legato licks are achieving 4npc at 160bpm or 6npc at 100bpm. If you want to play faster but lack stamina try 10bpm faster than your regular tempo ceiling and have a one click playing pause after every two repetitions. Burst playing like this gets you experiencing high tempos without straying due to fatigue.
Another option is to have a set tempo (say 100 bpm) and then ascend and descend through scales, shifting between rhythmic divisions; 2npc, then 3npc, then 4npc, then 6npc before winding back down to 2npc again.
An approach I like is to take a specific rhythm (eg ¼ note followed by two 1/8th notes) and apply it to a scale. This sounds a little more musical (there's variation!) and introduces a rhythmic discipline that may throw up one or two technical hiccups (eg cross picking) = a new practice area awaits!
You shouldn't just work with single notes though; make sure you spend as much time with your doublestop riffs and chord strumming. Use steady alternate picking and see how you can improve clarity and tempo flexibility with your favourite guitar parts. Even with a regular 16th note funk rhythm you can add syncopated colour by missing out some strums (ghost strums are performed but not heard) to create a more vibrant rhythm.
Try missing out the third 16th of each beat for two beats then the first 16th of each beat (final two beats in a 4/4 bar). Afterwards, combine this with a few different rhythmic divisions (eg 1/8th notes and sexptuplets) during a two bar 4/4 pattern and you'll have a part that is both challenging to play and fun to listen to.
For those that think rhythmic improvement is only about increasing tempo try this: set the metronome to 60bpm and try 'burying the click'; your placement on the beat is bang in the middle of the click's sound, masking it. It's quite a challenge as bigger the gap between clicks, the more elusive 100% accuracy can be.