I have a Joovy caboose and it pushed like a luggage cart. I will be putting it on Craigslist shortly. I recently got an Indie Twin and LOVE the push and use with my just turned two year old and newbie.
If I had an older one that still rode I'd get a buggy board for it.
I just saw a trimode double for 399 clearance plus a Joey seat for it fo 50 at local baby boutique. PM me if you want to know location. By coincidence I saw a three sweater in local used kids store and it looked like a train.
I'm not sure whether it works with a Graco (I haven't heard of anyone on here trying, but maybe someone knows more than I). But I was wondering how the Graco is to push with your two kids now? I fear that a buggy board may worsen the push of your current stroller.
Just a suggestion, but-
If you have a budget of about the $350 that the triple caboose costs (and perhaps you can sell you graco on CL), I would opt for a used double jogger (BOB, BJ, P&T etc.), and then grab the Valco hitchhiker, or similarly Lascal. This would improve your push immensely with three riders.
Just my 2-cents
We got the Graco as a gift so I'm sort of stuck with it. The push on it has never bothered me, even with my three year old in it. For as little as we use it I can't see DH wanting to spend $350 to buy another double, unless we can find it on CL.
Rebecca