Thanks for all your help. Sorry I forgot about this thread because my sim left IP and I just forgot about this issue. I have suspected earlier that disabling the trucks would still require me to simply delete the existing ones. I was really hoping there was something wrong with the truck issue because if this is not what is causing the pulse lags in IP, then I'm back to square one. Though I'm not using Ellacharm's fixed world, but I have read through it and gone through every house and houseboat manually to check if there are any errors.

As far as I can tell there shouldn't be anything causing the lag this bad. I reset the world a couple of times, but they would run smooth for less than a min before pulsing again. Putting in a subway to connect the two larger islands help, but now I'm wondering maybe I should put in more subway stops. I find it ridiculous that the sims rather boat around the island to reach the other island than cross it with a taxi to the subway stop.

Perhaps the IP lag is going to be forever a mystery.

I am pretty sure that Ellacharmed Fixes, goes a little further than only fixing houses and houseboats. On this link over at the SimsWiki you also see the extensive terrain fixes she made on the IP's global world map that can only be done in CAW, unsure if you have done that as well.

Though even if you got her IP version you still have to fix several houses/houseboats yourself, I think igazor knows which locations needs to be "fixed".

The obvious ones are Ichtaca, Los Amigos, Medina, and Scott (houseboat plus port). I didn't end up fixing any of these but replaced them all instead, though I did try (and failed miserably) with the nice looking Ichtaca castle before zapping it away. There are actually things wrong with many other lots in that world, such as the front being at the back, the wrong side being too close to a road so sims end up running all around the lot every time they enter/exit it, but I didn't detect any of those silly things causing lag or stutter while I was playing there, just inconvenience for their residents -- hey, if you want to live in paradise you might have to put up with such things. Ella's fixes were more valuable for the world lot glitches as reported. Other players have reported that they also needed to use an in-game cheat to remove the fog on undiscovered islands, but I never did that either.

Somehow I suspect that nitromon already knows about and has taken care of those things (and hopefully has Register, a must in that world) as there have been so many IP related threads over the years here and on MTS.

But maybe I just hadn't played IP long enough myself to experience all of its problems, it was really just over a sim week.