Nausea, vomiting, and delayed stomach emptying are areas where tolerance genuinely develops with GLP medications, so losing some of that tolerance across 8 weeks is plausible. It also matters somewhat which side effects you experienced when you raised your tirz doses in the past.
Clearly, the lowest risk approach is to begin with small doses and slowly work back up. Should you prefer to raise doses faster than the standard schedule, the safest route is using smaller, more frequent doses. This keeps each blood level peak lower, and blood levels will return to pre-dose values in only 2 or 3 days, meaning dosing twice weekly or every second day. As a restarting dose, 2.5mg twice a week is less likely to trigger troublesome side effects than 5mg once a week. It also allows for small dose bumps more often, for example 2.5 to 3.5 mg twice a week within a week or two, but if side effects do appear, it is important to slow or halt dose increases until things settle. Once you reach the weekly dose you want, you can gradually raise one half of the doses while lowering the other half until you are back to once a week. Before doing this, though, you need to check out glp plotter so you understand the drug pharmacokinetics, and attempting this without prior GLP drug experience is not such a great idea. When I switched from semaglutide to tirz, I used this process to go from 1mg to 15mg/week in a month. Generally, the faster you push dose increases, the higher the chance of unpleasant side effects.