I had uneven cut on Scag Cougar 48".....One of my blade mounting bolts had gotten slightly bent. And, the spindle was not 90 degrees to the deck. The deck is not very thick where the spindles mount , with the 3 bolts. I found the problem by measuring from tip of blade to the underside of the deck around the entire 360 degree...it was off quite a bit.
Couple things that will influence the cut, and will increase uncut strips:
1. Before leveling & pitching deck........properly inflate tires.
Have had customers get amazed at how it affects mower performance.
2. Floor MUST be level.
Need to start from a proper reference point.
3. Blade outer edges must be straight & square. I
If rounded....at the point where it changes from being straight & square to curved...you will LOSE that amount of cutting distance.
If the blade next to it is similar....you'll LOSE TWICE the cut! Example- say
the 'lost' cut is only 3/8". It will now be 3/8" + 3/8" = 3/4". The deck has a
1" overlap, but now only has 1/4" overlap.
4. If under cutting the blade bottom (tapering), it can lose 30-50 % air flow!
This is a bad practice we see alot of. Also comes from filing-grinding too
much blade material when removing the burr.
5. Blade simply sharpened wrong or worn out.
ANY blade that has 1/3 of it's width removed, or another way of saying it
is...is now only 2/3's as wide as a new blade when measuring from the
blade front edge to the rear...can LOSE up to 50% of it's air flow, and lift!
6. Engine speed too low.
7. Blade speed too low.
A. Loose belt idler pulley not having enough movement-tension.
Caused by worn parts....and sorry to say....lack of correct grease, and
not being greased enough.
B. Worn belt....worn drive pulley. Cast iron pulleys are known for this. A
belt must slide into the pulley "V" w/o sticking, and 'release' as it leaves.
If it pulls in too much....it binds. easily seen when comparing new vs.
worn, the belt tempature rises (using an infra red tempature tester).
c. Worn belt.....look for very shiny sides. Look for weat at the belt top
edge. look for damage to the fabric, or shinny (burn) spots.
8. Blades, and mowing technique used aren't suited for grass type.
There isn't one type deck, or one blade that wioll work in ever type grass,
or every type application. The only magic is in how some companies
advertise, or write the sales literature. Even how some reps & dealers sell.
Remember why Pinochio's nose grew?
Leveling & pitch are two different things that will affect mower performance, but usually will have poor over all cut performance, especaily discharge problems like clumping, and poor broadcasting.
You haven't mentioned these so I think the main problem is elsewhere.