Maybe consider having some of those trees removed, thus allowing for more room to actually get a ZT mower (or any other type of mower for that matter) with a large enough deck (like 60"-80") to not only cut the properly but also to allow less time cutting?
Yes at first it would be a bit time consuming and maybe a bit of $ having to remove some of those trees but in the long run, it'll make cutting that 4 acre property so much easier and less time consuming.
Last.....invest in a good quality ZT commercial mower with the ability to handle slopes.
If you were to do those things, it would definitely make life a lot better, for you.
Your choice.
Just my $0.02
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