heat soaked only after 2 hard pulls

Well I noticed the heat soaked with only 2 hard pulls. Just bolt on mods and ebay style side mount with racerx intercooler pipes. Whe ifirst drive it pulls hard and I hit 16 psi easy. By the time I do do 3rd pull it's heat soaked and I struggle to h 8 psi. Do people with side mounts hav this issue?

Do you have a shroud on the front of the air dam and a shroud on the back to a 9" aftermarket fan?

The intercooler needs air trapped and forced through it, hence the need of the above. In saying that I don't think that's your only issue to not be getting boost, however too many variables to say what it would be.

I think the mr2 club member sells (if he still has stock).... Or find by search engine fan group buy.... Club member totenkopf

If you are over boosting its a straight forward diagnose, not a dump pipe issue.
If your running an electronic boost controller, it is most probable your boost setting is incorrect in the set up; remembering a .5 setting is usually a 1.5 times than your wastegate actuator setting - so factory say 7psi, then it will boost to 14psi and 17psi after 4100 rpm. So you want your setting as low like .1
So if the boost controller set up is correct in the setting of what equates to the low or high then you need to check the movement of your wastegate actuator. Is it factory or aftermarket? Ensure the rods its attached to the hot side of the turbo / wastegate. Using a long long noise pair of pliers see if you can get it to move (it will only move about 7mm). If it moves slightly then all is good, if it doesn't move you have an issue with your wastegate being stuck or wastegate actuator being stuffed.
If it moves; Replace your pipe from your turbo bleed valve and put it straight to the wastegate actuator. Go for a drive and see what it does.
Lots of google results for wastegate actuator diagnose
Hope it helps or get it to a mechanic -
over boost = boom = new engine