Resetting my router to get the same results (or the SUT?)

I run a simulation and it works just fine, but the second time I run it I get timeouts (and shitty response times).
restarting my (wifi router) I get no timeouts (and good response times).
this pattern (in my opinion) seems to be that my ISP is the problem.

If I have a scenario which is very simple:



import io.gatling.core.Predef._
import io.gatling.core.scenario.Simulation
import io.gatling.http.Predef._
import scala.concurrent.duration._

class idpSimulation extends Simulation{

  val httpConf = http
    .headers(Map("Content-Type" -> "application/x-www-form-urlencoded; charset=utf-8"))
    .authorizationHeader("Basic bW9iaCxlX2NsaWVudFptb2JpbGVfc2VjcmX0")

  val scn = scenario("Scenario")




  setUp(scn.inject(constantUsersPerSec(150) during (20 seconds))).protocols(httpConf)


My question is (I hope I do not get an answer that suggests to check my ISP).

Could this be Gatling, or is this the SUT or my Broadband).

BTW: the SUT is not under very certain stress (CPU-wise).

Do I need to close the session(per session) or disable keep alive(?) to find the source of the challenge?
which strategy would you fetch to deal with the issue?