New lower unit...now boat porpoises at low speed

[Chico and the boys]

I have a 6" Atlas Jackplate on a 2001 225 Opti. When I take off, my trim is all the way down and once I get on plan I try to move the trim a little (as I could before) but as soon as do, it wants to porpoise. I don't remember my boat doing this before the new (rebuilt) lower unit. I am noticing this more now because of the fact that I am in the break in period and running under 3500 rpm's. Could there be a difference in the lower unit that is causing this.

[mdtritn21]

Did you just rebuild your old case?

[Chico and the boys]

Sorry about the late response. A complete rebuilt lower unit was installed, case and all. It is an SEI rebuilt unit.

[mdtritn21]

SEI case good luck.

[Chico and the boys]

Yeah I'm getting a lot of that. Hoping for the best.