Russian толкать might be related, sorry to be vague.
Yes, it seems that you're right. I've finally found a possible explanation
on this forum. I'll translate and report here the answer of user maksymus (my additions
in red):
From sъ-tlъkati («с-толкати», compare with Russian
столкнуть «to push off»). The labialization of л
to в is well recognizable (
compare, e.g., Russian волк 'wolf' and колбаса 'sausage' to Ukrainain вовк, ковбаса). The transformation into [š] was, perhaps, analogous to
шкаралупа (=eggshell, Russian скорлупа), кошлатий (=shaggy, Russian косматый), шпиця (=spoke, rung, Russian спица); possibly under Polish influence (compare:
штурхати '(Ukr.) to push'— szturchać '(Pol.),'to prod, to nudge' ).
BTW according to the Polish dictionary by Boryś szturchać comes probably from Middle High-German 'stürn' 'to dig around, to pick, to poke' so it's not directly related to штовхати.