change the oil and filter

it will go up and down with the rpm going up and down.

mine when cold is 60 psi steady with low and high rpm till it warms up good.

then it drops to 30 psi at idle in gear and will go up to 50-55 psi with the rpm going up to speed,drops when it comes back down.

it is kinda normal for it to do that. IMO

cut the old filter to see if it has any metal shavings or debrie