Outer Limits 4x4 Board

I have a 91 nh 3 litre Pajero that appears to have lost power compared to a while ago, it really slows down up hills without a load and is using about 15% more fuel, it's had both heads done, [head gasket blown] but this problem exsisted before then and is still there, any pointers on common problems with these symptoms would be appreciated, Rhys.

Blocked exh, dragging caliper, not getting full throttle, blocked intake system. Standard mech. checks
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