The adjusters are new and not broken in.

Operate the seat to full-forward and full rearward positions several times. This will work the new tightness out of the channels.

The adjusters are improperly lubricated.

Lubricate the adjuster channels using Lubriplate Auto-Lube A or an equivalent.

The adjusters bind due to being bent or from damaged channels.

Replace the adjuster.

The adjusters are not in parallel alignment with each other.

Loosen the floor pan attaching bolts or nuts. Align the adjusters so that the adjusters are parallel on the floor pan. Retighten the nuts.