Abstract: Reciprocating fluid pumps include a pump body including a cavity therein, a plunger located at least partially within the cavity, and a shift canister assembly disposed within the cavity. The shift canister assembly includes a sealing surface for forming a seal against the pump body. An area covered by the seal between the sealing surface and the pump body is less than about 75% of an outer cross-sectional area of the shift canister assembly. The shift canister assembly may include a shift canister and a shift canister cap attached thereto, the shift canister cap comprising the sealing surface. Reciprocating fluid pumps include a shift canister, a shift piston at least partially disposed within the shift canister, and a shift canister cap attached to the shift canister on a longitudinal end of the shift canister opposite the shift piston. Methods include forming such reciprocating pumps.